Veeam will be failing on the backups with the following log event:
Failed to create change tracking time stamp for virtual disk file..
After Googling the error, I found the official answer here. The page describes the issue but only offers one solution if it continues to happen:
Import the Veeam Module in Powershell and run
Reset-HvVmChangeTrackingon the Virtual Machine that is generating the error. This resets the change block tracking for that VM. Note that this also happens when you upgrade to a new version of Veeam as well.