Calendar keeps crashing

Outlook keeps saying "Not Responding" and crashes when a user works on calendar. This happens both in outlook client and outlook on the web. Here is what i have tried to do to fix the issue but it still persists.

• Ran outlook in safe mode
• Changed pc for the user
• Recreated user profile
• Also disabled add-ins.

Although I'm thinking this is a mailbox issue or some service incidence. Anybody here with similar issues and how was it resolved?

The error shown by outlook  "The Program Outlook.exe version xxxx stopped interacting with Windows "