Hi Charlie!
Thanks for reaching out to us. Let me help you troubleshoot that issue.
That seems like there could be a Javascript conflict. Could you please see if there are any console errors while on the edit event page? Here’s an article on how you can do that > https://theeventscalendar.com/knowledgebase/using-google-chrome-developer-tools/
If you don’t get any console errors, please enable WP_DEBUG and WP_DEBUG_LOG. This will create a debug.log file inside the /wp-content directory.
After that, try reproducing the issue a few times, so that in case there is an error, it will be saved into the debug.log file. Please share that log file with us so we can see if any problem from there.
Thanks,
Victor