thank you very much for your write up on ‘invalid_grant’ issue. Had the same problem with a few accounts last night and in search for solution found your article. Unfortunately, I have not been able to identify what the root cause was. Affected users haven’t revoked access or changed password, server clocks are in sync, api quota hasn’t been broken, etc. After approx. 12 hours of these errors (for random users), it didn’t happen again. For now, I’ll assume it was Google Drive API issue.