JS FullCalendar Recurring Event not having correct start time

first time posting here. I am using Javascript FullCalendar and I am trying to set up a simple recurring event. The problem is that its start time is not displayed correctly and the event itself is not appearing in the Week/Day View(I am assuming it’s because the start/end times are not being rendered correctly.) The recurring event is the one with title – Mathemathics. As show in the pictures, it displays a time of 12:00:00 which is incorrect as in the code I clearly set it to 16:00. It can be seen in the month view but in week and day it’s not showing up. Any tips and suggestions will be helpful, looked up all over the internet and the FullCalendar docs but couldn’t find anything related to my problem.

document.addEventListener('DOMContentLoaded', function() {
                var calendarEl = document.getElementById('calendar');
                var calendar = new FullCalendar.Calendar(calendarEl, {
                    initialView: 'dayGridMonth',
                    height: "90%",
                    slotMinTime: "06:00:00",
                    slotMaxTime: "20:30:00",
                    firstDay: 1,
                    eventTimeFormat: {
                        hour: '2-digit',
                        minute: '2-digit',
                        second: '2-digit',
                        meridiem: false
                    },
                    slotLabelFormat: {
                        hour: '2-digit',
                        minute: '2-digit',
                        meridiem: false,
                        hour12: false
                    },
                    headerToolbar: {
                        left: 'prev,next today',
                        center: 'title',
                        right: 'dayGridMonth,timeGridWeek,timeGridDay'
                        },
                    events: [{
                        title: 'Mathematics',
                        starTime: '16:00:00',
                        endTime: '17:30:00',
                        daysOfWeek: [1]
                    }, {
                        title: 'C++',
                        start: "2021-12-11T10:00:00",
                        end: "2021-12-11T12:00:00",
                    }]
                    });
                calendar.render();
            });

Month view

Week view

EDIT:
I am using FullCalendar v5.10.1