Hey there!
Ben here from the monday.com CRM team. It sounds like you may have a connection issue between gmail and monday.com. Revoking access, and then re-syncing usually does the trick.
Here is an article on how to revoke access from outlook side - How to Revoke Third-Party Access to Your Microsoft Account
If the issue is happening with Gmail, you can follow the instructions here- Gmail connection error
Once you have done that, you can recreate the connection, and the issue should be fixed.
If not, please reach out to support@monday.com, and they will be more than happy to look into this further