Using Classic Outlook on Windows for personal email, calendar, and contact management
My company has been having the same issue, I believe it has something to do with the Microsoft teams add in.
- Remove the "Microsoft Teams meeting Add on"
- go to Calendar Properties and clear offline items, then closed outlook.
- Re-add the Microsoft teams meeting add on, then close outlook.
- Open outlook and you should be good to go.
This fix has worked for us so far.