Hi, Kate. Sorry you’re experiencing this.
Whenever troubleshooting, it’s best to enable WP_DEBUG and WP_DEBUG_LOG (which will create a file on your server at /wp-content/debug.log if there are any WP_DEBUG messages) and share any debug messages you see while trying to replicate this issue. Please let me know any errors you generate when triggering this 500 error.
FYI: I imported your system information and saw you have Event Tickets Extension: PDF Tickets version 1.1.0 and also the DK PDF version 1.9.6 plugin. If you’re not using DK PDF for anything else, our PDF Tickets plugin does not rely on it.