A Backup contains a VM with Windows 2016 (or 2019) as the GuestOS and Deduplication is enabled for some (or all) of the drives. The Backup completes without Warnings or Errors, but when performing a Windows File Level Restore, you receive the following message:
Failed to transfer C:\VeeamFLR\VMName_index\Volume#\filename. The revision level is unknown.
Clicking ‘Continue’ skips the file.
If you navigate to C:\VeeamFLR and the locate the same volume, the file will be seen, but it won’t be restorable, producing the error: Error 0x80070519: The revision level is unknown.
If possible upgrade the OS of the Veeam Backup & Replication server and Mount server to one that matches or is newer than that of the OS that is contained in the backups, and then enable the Deduplication features.
As a workaround, the Veeam Backup & Replication console and the repositroy Mount server can be installed on a separate server which is running the compatible OS and feature set. This will allow the Veeam Backup & Replication server OS to remain unchanged.
To workaround this issue, please do the following:
After making these changes, restores should be successful.