Vue 3 + Vue I18n: “Not found key” error only on one page, works fine elsewhere

Issue Overview
I’m using Vue 3 and Vue I18n (version 9.x) in my project. All of my pages are translating keys correctly except for one page, where it fails to find the translation keys for sustainabilityPage. I keep seeing console warnings like:

[intlify] Not found 'sustainabilityPage.sections.rAndD.title' key in 'tr' locale messages.
[intlify] Fall back to translate 'sustainabilityPage.sections.rAndD.title' key with 'en' locale.

Despite the fact that I have sustainabilityPage definitions in my tr.json (and en.json) files, it just won’t translate on this page.

Vue I18n Configuration (i18n.js)
import { createI18n } from 'vue-i18n';
import tr from './locales/tr.json';
import en from './locales/en.json';

const i18n = createI18n({
  legacy: false, // for Vue 3 Composition API
  locale: 'tr',  // default language
  fallbackLocale: 'en',
  globalInjection: true,
  messages: {
    tr,
    en
  }
});

export default i18n;

Main.js
import { createApp } from 'vue';
import App from './App.vue';
import router from './router';
import i18n from './i18n';

const app = createApp(App);
app.use(i18n); // using Vue I18n
app.use(router);
app.mount('#app');

Problematic Component (Sürdürülebilirlik.vue)

<template>
  <div
    class="about-page"
    :style="{ backgroundImage: 'url(/assets/img/fabrika.jpg)' }"
  >
    <div class="overlay"></div>
    <div class="container mx-auto px-4 py-12">
      <!-- Section 1 - Ar-Ge Merkezi -->
      <div class="flex flex-wrap items-center mb-12 fade-in">
        <div class="w-full md:w-5/12 ml-auto mr-auto px-4">
          <div class="card">
            <h3 class="text-2xl font-semibold text-white">{{ $t("sustainabilityPage.sections.rAndD.title") }}</h3>
            <p class="mt-4 text-lg leading-relaxed text-gray-200">
              {{ $t("sustainabilityPage.sections.rAndD.description1") }}
            </p>
            <p class="mt-4 text-lg leading-relaxed text-gray-200">
              {{ $t("sustainabilityPage.sections.rAndD.description2") }}
            </p>
          </div>
        </div>
        <div class="w-full md:w-4/12 ml-auto mr-auto px-4">
          <img
            src="/assets/img/resim2.jpg"
            :alt="$t('sustainabilityPage.sections.rAndD.title')"
            class="max-w-full rounded-lg shadow-xl transform transition duration-500 hover:scale-105"
            loading="lazy"
          />
        </div>
      </div>

      <!-- Section 2 - Yenilenebilir Enerji -->
      <div class="flex flex-wrap items-center mb-12 flex-row-reverse fade-in">
        <div class="w-full md:w-5/12 ml-auto mr-auto px-4">
          <div class="card">
            <h3 class="text-2xl font-semibold text-white">{{ $t("sustainabilityPage.sections.renewableEnergy.title") }}</h3>
            <p class="mt-4 text-lg leading-relaxed text-gray-200">
              {{ $t("sustainabilityPage.sections.renewableEnergy.description1") }}
            </p>
            <p class="mt-4 text-lg leading-relaxed text-gray-200">
              {{ $t("sustainabilityPage.sections.renewableEnergy.description2") }}
            </p>
          </div>
        </div>
        <div class="w-full md:w-4/12 ml-auto mr-auto px-4">
          <img
            src="/assets/img/resim3.jpg"
            :alt="$t('sustainabilityPage.sections.renewableEnergy.title')"
            class="max-w-full rounded-lg shadow-xl transform transition duration-500 hover:scale-105"
            loading="lazy"
          />
        </div>
      </div>

      <!-- Section 3 - Atık Su Arıtma -->
      <div class="flex flex-wrap items-center mb-12 fade-in">
        <div class="w-full md:w-5/12 ml-auto mr-auto px-4">
          <div class="card">
            <h3 class="text-2xl font-semibold text-white">{{ $t("sustainabilityPage.sections.wasteWaterTreatment.title") }}</h3>
            <p class="mt-4 text-lg leading-relaxed text-gray-200">
              {{ $t("sustainabilityPage.sections.wasteWaterTreatment.description1") }}
            </p>
            <p class="mt-4 text-lg leading-relaxed text-gray-200">
              {{ $t("sustainabilityPage.sections.wasteWaterTreatment.description2") }}
            </p>
          </div>
        </div>
        <div class="w-full md:w-4/12 ml-auto mr-auto px-4">
          <img
            src="/assets/img/resim4.jpg"
            :alt="$t('sustainabilityPage.sections.wasteWaterTreatment.title')"
            class="max-w-full rounded-lg shadow-xl transform transition duration-500 hover:scale-105"
            loading="lazy"
          />
        </div>
      </div>

      <!-- Section 4 - Enerji Üretimi -->
      <div class="flex flex-wrap items-center mb-12 flex-row-reverse fade-in">
        <div class="w-full md:w-5/12 ml-auto mr-auto px-4">
          <div class="card">
            <h3 class="text-2xl font-semibold text-white">{{ $t("sustainabilityPage.sections.energySolutions.title") }}</h3>
            <p class="mt-4 text-lg leading-relaxed text-gray-200">
              {{ $t("sustainabilityPage.sections.energySolutions.description1") }}
            </p>
            <p class="mt-4 text-lg leading-relaxed text-gray-200">
              {{ $t("sustainabilityPage.sections.energySolutions.description2") }}
            </p>
          </div>
        </div>
        <div class="w-full md:w-4/12 ml-auto mr-auto px-4">
          <img
            src="/assets/img/resim7.jpg"
            :alt="$t('sustainabilityPage.sections.energySolutions.title')"
            class="max-w-full rounded-lg shadow-xl transform transition duration-500 hover:scale-105"
            loading="lazy"
          />
        </div>
      </div>
    </div>
  </div>
</template>

<script>
import { useHead } from '@vueuse/head';
export default {
  name: "Sürdürelebilirlik",
  setup() {
    useHead({
      title: 'Kahramanmaraş Kâğıt - Ar-Ge ve Sürdürülebilirlik Çözümleri',
      meta: [
        { name: 'description', content: 'Kahramanmaraş Kâğıt olarak, Ar-Ge merkezi, yenilenebilir enerji yatırımları, atık su arıtma tesisimiz ve biyokütle enerji tesisimizle çevre dostu ve sürdürülebilir çözümler sunuyoruz.' },
        { name: 'keywords', content: 'Kahramanmaraş Kağıt, Ar-Ge Merkezi, Biyokütle Enerji Tesisi, Atık Su Arıtma, Sürdürülebilir Enerji, Güneş Panelleri, Yenilenebilir Enerji, Enerji Verimliliği, Çevre Dostu Üretim' },
        { property: 'og:title', content: 'Kahramanmaraş Kâğıt - Çevre Dostu ve Yenilikçi Çözümler' },
        { property: 'og:description', content: 'Yüksek enerji verimliliği ve çevre dostu teknolojilerle sürdürülebilir üretim yapıyoruz. Tesisimizde yenilikçi enerji çözümleri uyguluyoruz.' },
        { property: 'og:image', content: '/assets/img/fabrika.jpg' },
        { property: 'og:type', content: 'website' },
        { property: 'og:url', content: 'https://kahramanmaraskagit.com/surdurulebilirlik' },
        { name: 'twitter:card', content: 'summary_large_image' },
        { name: 'twitter:title', content: 'Kahramanmaraş Kâğıt - Sürdürülebilir Enerji ve Ar-Ge Çalışmaları' },
        { name: 'twitter:description', content: 'Ar-Ge merkezimiz ve enerji üretim tesislerimizle fark yaratıyoruz.' },
        { name: 'twitter:image', content: '/assets/img/resim2.jpg' },
        { name: 'viewport', content: 'width=device-width, initial-scale=1.0' }
      ]
    });
  }
};
</script>

<style scoped>
.about-page {
  position: relative;
  min-height: 100vh;
  background-size: cover;
  background-position: center center;
  background-attachment: fixed;
  color: white;
  overflow: hidden;
}

.overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.4);
  z-index: 1;
}

.container {
  margin-top: 100px;
  position: relative;
  z-index: 2;
}

.card {
  background-color: rgba(0, 0, 0, 0.6);
  backdrop-filter: blur(8px);
  border-radius: 10px;
  padding: 20px;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
}

img:hover {
  transform: scale(1.05);
  transition: transform 0.3s ease;
}

.fade-in {
  opacity: 0;
  animation: fadeInUp 1s ease-in-out forwards;
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}
</style>

Note: On other pages, $t(“someKey”) works perfectly. Only this page triggers “Not found” fallback warnings.

en.json

{
    "navbar": {
      "home": "Home",
      "corporate": "Corporate",
      "aboutUs": "About Us",
      "missionVision": "Mission and Vision",
      "products": "Products",
      "quality": "Quality",
      "sustainability": "Sustainability",
      "contact": "Contact",
      "career": "Career",
      "mediaCenter": "Media Center",
      "catalog": "E-Catalog"
    },
    
        "header": {
          "welcomeTitle": "Welcome to Kahramanmaraş Kağıt",
          "welcomeMessage": "Our company plays a significant role in the paper and packaging industry in Turkey. This position has been achieved over the years through the trust of our customers, suppliers, and employees."
        },

        "features": {
          "title1": "High-Quality Production",
          "desc1": "Kahramanmaraş Paper stands as a leader in the industry by producing paper under high quality standards. With an eco-friendly approach, we offer solutions that are conscious of the environment.",
      
          "title2": "Sustainability-Focused Production",
          "desc2": "Environmental awareness lies at the core of our business. The raw material we use in our factory is sourced entirely from 100% recycled waste paper. Thus, we help protect 6,000 hectares of forest area each year. We reinforce our commitment to the environment through advanced wastewater treatment systems and eco-friendly production processes at our facility.",
      
          "title3": "Building a Strong Future Together",
          "desc3": "At Kahramanmaraş Paper, we are not just producing paper; we are building a sustainable future with eco-friendly technologies. We continue to make a difference in the industry through our contributions to the regional economy, employment opportunities, and logistical advantages.",
      
          "title4": "Advanced Technology and R&D",
          "desc4": "For us, innovation is not only a goal but also part of our continuous development. Our R&D center works tirelessly to expand our product range and offer more innovative solutions to our customers. Every process in our factory is carried out in accordance with quality and safety standards.",
      
          "sectionTitle": "Working with Us Is a Privilege",
          "sectionDesc1": "At Kahramanmaraş Paper, we always prioritize customer satisfaction by adhering to the principle of providing high-quality products and services. We aim to build a long-term business partnership with you.",
          "sectionDesc2": "To learn more about our products, feel free to get in touch with us.",
          "sectionButton": "Get in Touch!",
      
          "quoteTitle": "Production with Evolving Technology",
          "quoteDesc": "By integrating technology into our production processes, we strengthen our competitive edge in the industry. We always strive to offer better and more efficient solutions."
        },

      
          "anafooter": {
            "companyName": "Kahramanmaraş Paper",
            "companyTagline": "Serving you with our Innovative and Eco-Friendly Approach.",
            "email": "[email protected]",
            "usefulLinks": "Useful Links",
            "home": "Home",
            "about": "About Us",
            "products": "Products",
            "equalOpportunities": "Equal Opportunities",
            "certificates": "Our Certificates",
            "contact": "Contact",
            "contactLocations": "Contact & Locations",
            "locationKahramanmaras": "Kahramanmaraş",
            "locationIstanbul": "Istanbul",
            "copyright":
              "© {year} Kahramanmaraş Paper Ind. and Trade Inc. All rights reserved.",
            "cookiePolicy": "Cookie Policy",
            "personalDataProtection": "Personal Data Protection",
            "informationSocietyServices": "Information Society Services",
            "cookiePreferences": "Cookie Preferences"
          },

          "about": {
    "pageTitle": "About Us",
    "paragraph1": "Kahramanmaraş Paper Industry and Trade Inc. was established in 1988 in Kahramanmaraş on an area of 200,000 m², of which 30,000 m² is enclosed.",
    "paragraph2": "Production of corrugated cardboard paper began at the end of 1989, with the PM1 paper machine that has an annual capacity of 40,000 tons.",
    "paragraph3": "In 1997, after investing in the PM2 paper machine, the company also began producing grey board. Later that same year, modernization of the PM1 paper machine not only improved quality ....,
    "paragraph4": "Since its foundation, Kahramanmaraş Paper has stood out by delivering solutions for the corrugated cardboard sector. Today, it serves domestic and international markets with Fluting, Test Liner, Grey Board, Plasterboard Paper, and various specialty paper grades.",
    "paragraph5": "Continuous operations in our R&D Center form a key dynamic of our growth. Under the principle of Total Quality, we pursue activities aimed at meeting the ....
      },
       
      "visionMission": {
        "pageTitle": "Our Mission and Vision",
    
        "mission": {
          "title": "Our Mission",
          "desc": "To recover waste paper from the environment and contribute to leaving a better world for future generations, while utilizing high technology and modern ....
        },
    
        "vision": {
          "title": "Our Vision",
          "desc": "To transform our company into an exemplary leader in the paper industry, one that adopts reliability, respectability, and customer satisfaction as its fundamental ....
        },
    
        "missionImageAlt": "Eco-friendly production mission image",
        "visionImageAlt": "Green production and zero waste vision image"
      },
      
      "footer": {
            "companyName": "Kahramanmaraş Paper",
            "companyTagline": "Serving you with our Innovative and Eco-Friendly Approach.",
            "email": "[email protected]",
            "usefulLinks": "Useful Links",
            "home": "Home",
            "about": "About Us",
            "products": "Products",
            "equalOpportunities": "Equal Opportunities",
            "certificates": "Our Certificates",
            "contact": "Contact",
            "contactLocations": "Contact & Locations",
            "locationKahramanmaras": "Kahramanmaraş",
            "locationIstanbul": "Istanbul",
          },
      
          "productsPage": {
            "title": "Our Products"
          },

          "qualityPage": {
            "sectionTitles": {
              "politikalar": "Our Policies",
              "ilkeler": "Our Principles",
              "eys": "Integrated Management System (IMS) Policy",
              "sosyal": "Social Compliance",
              "firsat": "Equal Opportunity",
              "sertifika": "Our Certificates"
            },
            "ilkeler": {
              "introHtml": "As Kahramanmaraş Paper Industry and Trade Inc., we carry out our activities within the framework of the core principles and values we embrace; with our focus on innovation....
              "listItems": [
                "Being a trusted company",
                "Continuously improving our processes and services",
                ...
                "Adhering to social responsibility and universal ethical values",
                "Giving importance to continuous training and development at every level",
                "Being a fast, agile, successful, results-oriented, and industrious company",
                "Setting an example for the best business practices in the paper industry",
                "Offering the best to our customers as quickly as possible with a ...
                "Being open to continuous improvement by tracking innovations and producing innovative products and ideas",
                "Carrying out deep-rooted, tradition-based corporate values on the basis of fairness, transparency, and mutual trust",
                ....
            },
            "eys": {
              "introHtml": "Kahramanmaraş Paper Industry and Trade Inc. acknowledges that the success of its activities is highly dependent on the quality, occupational health and safety, environment, and energy management systems it implements. Therefore, Integrated Management Systems will always be prioritized.",
              "paragraphs": [
                "As one of the leading players in the paper industry in our country, we aim to add value to all our stakeholders and contribute to sustainable development by conducting our paper production and trade activities in accordance with international standards.",
                "Our company, in line with its Quality, Environmental, Occupational Health and Safety, and Energy Management Systems, is committed to the following policies:"
              ],
              "listItems": [
                "Complying with legal and other requirements",
                "Ensuring continuous customer satisfaction",
                "Sustaining continuity and sustainability in all operations",
                "Supporting and improving suppliers and business partners",
                "Taking measures to enhance energy efficiency and conservation",
                "Constantly improving production efficiency and overall performance",
                "Respecting people and the environment by focusing on sustainability",
                "Ensuring effective, economical, and efficient use of all resources",
                "Providing necessary knowledge and resources to achieve set goals and objectives",
                "Preventing pollution, reducing waste, and increasing recycling rates",
                "Eliminating hazards, effectively managing risks and opportunities",
                "Creating an open communication environment for employee participation",
                "Complying with applicable legal and other requirements regarding energy efficiency, usage, and consumption",
                "Enhancing collaboration and transparency among stakeholders",
                "Considering quality, OHS, environmental, and energy performance in all design and procurement processes",
                "Implementing and continuously improving the ISO 9001, ISO 14001, ISO 45001, and ISO 50001 standards",
                "Structuring the Integrated Management System based on risk-based thinking, ensuring sustainability",
                "Providing comprehensive training to enhance awareness of all IMS-related standards",
                "Prioritizing the health and safety of employees over profitability, working towards a 'zero accident' goal"
              ],
              "chairmanLine": "Chairman of the Board: Muhammet Muhittin CİĞER"
            },
            "sosyal": {
              "introHtml": "<strong>As KAHRAMANMARAŞ PAPER IND. AND TRADE INC.,</strong>",
              "paragraphs": [
                "Our social compliance policy includes standards that we have created in collaboration with all our business partners based on fundamental principles and values, and implemented as a team effort. Our goal is to integrate the Social Compliance Policy into our corporate culture. Therefore, social compliance standards have been established and put into practice.",
                "In addition to creating products and services through these social compliance standards, this policy commits to providing employees with all rights derived from legal standards, complying with occupational health and safety rules, being environmentally conscious, and fostering an open and honest communication environment where employees feel valued and respected.",
                "The social compliance policy is communicated to all our employees through training sessions or communication channels (notice boards, website, email groups, etc.). Our suppliers are informed,.......
                "The Social Compliance Policy includes the following components:"
              ],
              "listItems": [
                "Prevention of Child Labor",
                "Prevention of Forced and Compulsory Labor",
                "Ensuring Occupational Health and Safety and Its Sustainability",
                "Respect for Freedom of Association, Representation, and Collective Bargaining Rights",
                "Prevention of Discrimination (Equal Treatment Approach)",
                "Recruitment and Regular Employment",
                "Prevention of Discipline, Harassment, and Ill-Treatment",
                "Raising Employee Awareness",
                "Communication of Requests and Complaints",
                "Working Hours",
                "Wages and Payments",
                "Compliance with Laws and Other Obligations",
                "Anti-Bribery and Corruption",
                "Supply Chain Management"
              ],
              "closingParagraph": "Kahramanmaraş Paper Ind. and Trade Inc. undertakes to carry out its social compliance activities in accordance with the applicable laws and regu....
              "chairmanLine": "Chairman of the Board: Muhammet Muhittin CİĞER"
            },
            "firsat": {
              "introHtml": "<strong>As KAHRAMANMARAŞ PAPER INDUSTRY AND TRADE INC., we value equal opportunity and diversity.</strong>",
              "paragraphs": [
                "Kahramanmaraş Paper Industry and Trade Inc. Equal Opportunity Policy defines our company's responsibilities and principles regarding equal opportunity applications, covering all employees and activities. Our company is aware of the great benefits of understanding, evaluating, and effectively managing differences at the individual, team, and corporate levels in achieving success."
              ],
              "listItems": [
                "Our organization respects human rights and upholds the principle of equality for all employees.",
                "In all human resources applications, including recruitment, promotion, and development decisions, we do not discriminate based on religion, language, race, or ethnic origin, and we prioritize collective intelligence within the company.",
                "We stand against any form of discrimination or harassment directed at our employees or occur.....
                "We do not discriminate based on gender, religion, sect, race, marital status, political opinion, disability status, social class, philosophical beliefs, or other visible or invisible....
                "We aim to increase the employment rate of women within the company and in managerial positions and strive to ensure gender equality at every management level.",
                "By fostering a high-performance culture, we support employees' professional and personal development through continuous education and feedback.",
                "We adopt an 'Equal Pay for Equal Work' policy and monitor related indicators.",
                "We promote the principle of equal opportunity among all employees through various training programs and social responsibility projects.",
                "Kahramanmaraş Paper strives to ensure that the Equal Opportunity Policy is communicated to all stakeholders.",
                "The Human Resources Department and Managers are responsible for tracking compliance with every aspect of the Equal Opportunity Policy at Kahramanmaraş Paper."
              ],
              "chairmanLine": "Chairman of the Board: Muhammet Muhittin CİĞER"
            },
            "sustainabilityPage": {
            "title": "R&D and Sustainability Solutions",
            "sections": {
              "rAndD": {
                "title": "Our R&D Center",
                "description1": "Our R&D Center was registered as Turkey's 576th R&D Center by the Ministry of Industry and Technology on December 13, 2017. A team of approximately 25 experts in six different departments conducts studies in process development, product innovation, energy efficiency, and intellectual property.",
                "description2": "By collaborating with universities and other R&D centers, we have successfully completed many national and international projects, such as TÜBİTAK projects, leading technical and technological developments."
              },
              "renewableEnergy": {
                "title": "Our Renewable Energy Investments",
                "description1": "As Kahramanmaraş Paper, we invest in renewable energy sources as part of our environmentally friendly production approach. Thanks to the solar panels installed at our factory facilities, we meet a significant portion of our energy needs using environmentally friendly and sustainable methods.",
                "description2": "This system optimizes energy costs, enabling us to achieve more efficient production. With our future projects, we will continue to support environmental sustainability."
              },
              "wasteWaterTreatment": {
                "title": "Our Wastewater Treatment Facility",
                "description1": "We prioritize the efficient use of water resources by adopting an environmentally friendly production approach in our factory. At our wastewater treatment facility, water generated from our production processes is treated using modern methods and reused in production.",
                "description2": "Thus, we reduce our reliance on natural water resources and contribute to environmental sustainability. Through continuous improvement and innovative technologies, we strive to make the most efficient use of our resources."
              },
              "energySolutions": {
                "title": "Innovative Solutions in Energy Production",
                "description1": "Our Kahramanmaraş factory is not only a production facility but also a plant that generates its own energy. Our 11 MW cogeneration plant provides the energy needed for our production processes, reducing our dependence on external sources.",
                "description2": "Additionally, our newly commissioned biomass energy plant significantly contributes to our factory’s environmental sustainability goals. By producing energy from organic waste, we both reduce our carbon footprint and adopt an environmentally friendly approach."
              }
            }
          } 
        }      
}

What I’ve Tried
Verified that all other pages correctly pick up $t(“…”) keys.
Inserted a console.log(“Testing key:”, this.$t(“…”)); in mounted(), which returns undefined or “Not found… key in ‘tr’ locale messages.”
Checked that tr.json does contain sustainabilityPage exactly as above.
Also tried console-logging window.i18n?.global.messages.value.tr, which shows undefined on this route, but not on others.
I’m using Options API on this component; my other components also use Options API and $t().

Question
Why does only this page fail to recognize sustainabilityPage.sections.rAndD.title while all other pages use $t() with no issues?
Could there be a route or instance conflict that means this component is not using the same i18n instance?
Any possible hidden reason that $t(“sustainabilityPage…”) can’t be found here?
Thanks in advance for your suggestions!