Hey Michele,
Thank you for reaching out to us! I’m very sorry about this issue you are experiencing.
I’ve verified that although your calendar is displaying this 404 error, the HTTP status for this page is HTTP/1.1 200 OK (you can check this by pasting your calendar URL (https://www.jenscom.com/dev/tha/events/) here).
So it seems that your calendar is loading as expected, but for some reason it’s being hidden/replaced by this generic 404 error.
Since you already ran the Conflict Test (deactivated all plugins, except TEC, and switched your current active theme to a WordPress default like Twenty Seventeen) and the issue persists, can you please please enable WP_DEBUG and WP_DEBUG_LOG and share with us any messages you see while accessing your Events page? All WP_DEBUG messages will be stored in a debug.log file in /wp-content/debug.log.
I hope this helps! Let me know your test results and I’ll be happy to further investigate your case if necessary.
Regards,
Patricia