After investigation I found that the DOM is not able to hook into the fullcal...

After investigation I found that the DOM is not able to hook into the fullcalendar library. And this is happening only for block.

I found that this this.$calendar.find('.fullcalendar').once().fullCalendar(this.$options) inside web/modules/contrib/fullcalendar/assets/js/fullcalendar.library.js is getting executed before the block is rendered.