Got a resolution to this:
I would like to see if clearing the SQL database will help get this backup running again for you. Here are the steps to set this up.
Step 1 - Open up RegEdit
Step 2 - Look for HKEY_LOCAL_MACHINE\SOFTWARE\Veeam\Veeam Endpoint Step 3 - Look for the DWORD value called ReCreateDatabase and assign to it 1 (decimal) Step 4 - Close regedit, open up the services.msc console, and re-start the Veeam Endpoint Backup service manually or just reboot the machine.
Please note that after performing these steps, it will be required to reconfigure the Endpoint backup. Also too, this will create a brand new backup chain. The previous chain may still be used for restoration purposes. But otherwise, can be discarded.
That seems to have worked. Since this was happening to other VMs, and these VMs are not yet in production, I did some other testing to try and troubleshoot the issue:
In Veeam B&R Console, I went to Backup & Replication, Backups, Disk and right-clicked on the VM and chose "Remove from configuration". I ran another backup and this time it was successful.
I think what caused this, is we disabled the backups from Veeam B&R Console for about 2 weeks. Maybe you guys can look into if people do this, that the backups can still complete successfully without having to delete the old restore points?