Hi, Nigel. Sorry you’re experiencing this.
I tried to replicate this on my local testing site but couldn’t.
Since this isn’t currently a known issue, I’d suggest following these recommended troubleshooting steps for your own site:
There might be some new updates available. 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 Twenty Sixteen 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 debug messages 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 re-share your System Information (while in Testing for Conflicts Mode). A link to your site and a video screen recording of you demonstrating the issue could help in this case too.
Let us know what you find out.
Thanks.