Splide.js options are not working except gap

I’m trying to add splide.js to my site. I’ve initialised the splide.js like this:

//initiate splide.js
            function initiateSplideElements() {
                var elms =
                    document.getElementsByClassName("plans-container");

                for (var i = 0; i < elms.length; i++) {
                    new Splide(elms[i], {
                        perMove: 1,
                        gap: "1.5rem",
                        mediaQuery: "min",
                        destroy: false,
                        perPage: 1,
                        breakpoints: {
                            960: {
                                perPage: 2,
                            },
                            1201: {
                                perPage: 3,
                            },
                        },
                    }).mount();

                    new Splide(".column-carousel", {
                        type: "loop",
                        perMove: 1,
                        gap: "1rem",
                        mediaQuery: "min",
                        destroy: false,
                        perPage: 1,
                        breakpoints: {
                            960: {
                                perPage: 2,
                            },
                            1201: {
                                perPage: 3,
                            },
                        },
                    }).mount();
                }
            }

            window.addEventListener("DOMContentLoaded", () => {
                initiateSplideElements();
            });

Although, the gaps are being applied, the arrows or breakpoints aren’t working. While resizing the page, for a moment the arrows become visible and then it vanishes again. Please click the ‘test plan popup’ at the bottom of this page to view the problem: buggy page

I had initialised the splide.js with the same options and content in this page and it is working (please scroll down and click the ‘test plan popup’ button).

I cannot figure out why the same splide is working in one page and not working in another. Please help.