The question states that "all the user account synchronizations completed successfully". If there were problems with the 10 accounts that needed fixing with idfix.exe, there would have been synchronization errors in Microsoft Entra Connect Health. It is likely that the 10 user accounts are being excluded from the synchronization cycle by a filtering rule. Reference: https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-sync-configure-filtering