MacOS calendar help!

[woodbane]

Hi all,

New to MacOS with a 2020 MacBook Air M1 and I've hit an annoying bug?

Adding my work Office 365 account and then syncing the calendar with the built in calendar app is causing multiple duplicated entries and showing entries that just shouldn't even be there!

I've attached screen shots of the same week period showing in the built in calendar app and the Outlook app - you can see the difference.

These entries only show in the MacOS built in calendar, everywhere else (iPhone, other mail apps on Windows PC's) things are showing correctly.

I've tried:

1. unchecking and re-checking the calendar to sync under Calendar - Preferences: duplicate entries just come back and there are sometimes more of them.
2. deleting and re-adding the office 365 work account completely, same problem persists.
3. deleting the calendar sub folders under ~Library/calendars: still getting the same.

Has anyone got any clue as to what's going on as it would seem a bit ridiculous I can't even use Apple's own built in calendar app and have to resort to using a third party one.

Any help is much appreciated.