Hi Anne!
Thanks for getting in touch with us! Let me help you with that issue.
Please first make sure you are using the latest versions of our plugins. Remember you can always get the latest versions by going to your downloads page > https://theeventscalendar.com/my-account/downloads/
If you still experience the error, 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.
Let us know how that goes.
Thanks,
Victor