When trying to use Microsoft Office on a device, users will sometimes experience a "Something went wrong. We couldn't sign you in" error screen with error code CAA50021. Server message: number of retry attempts exceeds expectation. This error can simply be resolved by signing out of the user's school email in Windows settings.
Select the dropdown next to your work or school account and select Disconnect.
Select Yes to confirm.
Then afterwards, sign in again with your LUNA credentials using the Connect button.