Hi. Thanks for your detailed question.
I noticed console errors at your site when doing what you described: https://cl.ly/1w183n1p0E3x
(If needed, you may reference our KB article Using Google Chrome Developer Tools.)
Therefore, since this isn’t default behavior, I’d suggest following our recommended troubleshooting steps:
Could you please make sure all your Modern Tribe plugins (and WordPress core) are at their latest versions?
Once you verify you’re on the latest versions, please test to see if the issue is still happening for you.
If it is, please follow our Testing for Conflicts Guide (basically switch to TwentySixteen theme and deactivate all plugins and custom code other than Modern Tribe plugins) and see if that helps narrow down the cause of this.
If it doesn’t, please enable WP_DEBUG and WP_DEBUG_LOG and share any PHP errors you see while changing tickets quantity, navigating your site’s home page, events page, single-event pages, and any other of your site’s pages relevant to this ticket.
Then, please share your System Information (while in Testing for Conflicts mode).
Let us know what you find out.
Thanks.