Hi Karly, if you downgrade the TEC core plugin to 3.12.3 it will fix the issue:
https://theeventscalendar.com/support/forums/topic/after-updating-the-events-calendar-from-3-12-3-to-3-12-4-filter-bar-ajax-broke/#post-1022384
After just purchasing the Filter Bar add-on and spending an hour trying to figure out why it wasn’t working out of the box, I eventually found that post. 🙂
Anyway, I wanted to ask… where is the “Use Javascript to control date filtering” checkbox? I’d like to have that option. I don’t see it anywhere in TEC Settings pages?