Hi and welcome back 🙂
I’m not really sure why you’re seeing the error. I see you checked ‘Yes’ to reverting back to the default WordPress theme and deactivating all plugins other than ours as instructed in the Testing for conflicts guide, but can you please confirm this?
It might be best you set up a fresh WordPress installation where you can fully troubleshoot the issue. Make sure you have only the default WordPress theme, The Events Calendar, and Community Events installed and activated on the test site. Please review our Using One License for Live and Dev Sites for more information.
Please make sure WP_DEBUG and WP_DEBUG_LOG are enabled on your site’s wp-config.php file. Any errors will display at the top of your page as you try to reproduce the conflict. Note what you find and please include it in your reply.
Another helpful resource in this situation is Our Favorite Developer Plugins article which goes over some plugins which can aid in diagnosing issues. Thanks and have a great rest of the weekend. Cheers!