Good evening Joanna and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the cleanup of recurring events not working on your site.
I would love to help you with this topic.
Is there a common reason for clean up recurring to not work? What is suggested to resolve this?
This most likely means that the Cron jobs that would perform that cleanup are not being triggered or that somehow they are blocked from execution.
You might want to give the following extension a spin to see if it helps: https://theeventscalendar.com/extensions/recurring-event-cleanup-tool/
You could also try to run a plugin such as https://wordpress.org/plugins/wp-cron-control/ to check on your various CRON jobs.
Let me know how that goes.
Best regards,
Geoff B.