Calendar app on Mac creating phantom events not on iCloud or iPhone

On my MacBook, the Calendar app is creating phantom duplicates of events on different days/times when iCloud and iPhone are both normal and do not have these phantom events. What is going on with the Mac app and how can I stop it?

More info: I am using CalendarBridge to share events to/from my iCloud account and an Outlook exchange calendar account. The iCloud calendar, the iPhone calendar, and the Outlook calendar are all correct. But the app on the MacBook creates duplicates of Outlook calendar events on different days, with different times and lengths of time, and puts them all over the place seemingly randomly.

I've logged out and back into iCloud on the Mac (restarting after each), turned off the Calendar in iCloud on the Mac and back on (again restarting after each). These actions have not solved or prevented this problem.

Any ideas?

Thanks!

Michele