Microsoft Graph API 403 - Could not obtain a WAC access token

Question

I have an integration with the Microsoft Graph API to read and write Excel files on OneDrive.

I am suddenly getting the errors:

HTTP Error occurred: 403 Client Error: Forbidden for url: https://graph.microsoft.com/v1.0/me/drive/items/%5C*%5C*%5C*/workbook/worksheets

Response Content: {"error":{"code":"AccessDenied","message":"Could not obtain a WAC access token.","innerError"....}}

I can still read the titles of the files through the API but cannot write to them. My code has not changed and my permissions are still the same with read/write.all etc and it was working less than 2 days ago.

I have tried removing the connection and re-authenticating, trying different Excel files, and ensuring they all have .xlsx extension however the error persists.