Hi,
Sorry for the issues.
We have a bug in the system that does not hide events from the month view if the hide from event listings is checked for an event.
We did not have a solid definition of what that meant and the developer removed it from the coding.
We have a maintenance release getting ready to ship next week that should fix the issue.
If you downgrade to 3.11 for all the plugins the issue can be resolve today and then you could update again once we release this fix next week.
You can follow the steps to manually update the plugins here:
Manual Updates
Let me know if we are talking about the same thing here or if you have any more questions.
Thanks