Hi,
Thanks for reaching out to us! I’d be happy to help you 🙂
First, could you please enable WP_DEBUG (https://codex.wordpress.org/Debugging_in_WordPress) and WP_DEBUG_LOG (https://codex.wordpress.org/Debugging_in_WordPress#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.
Then, could you share again your System Information (you may paste it as a “Private” reply to this mail)? For some reason, I only got the versions of your Event Tickets and The Events Calendar plugins.
Thanks in advance,
Jeremy