There is a CBT issue preventing incremental backups from working as expected as indicated in the job log.
----- Error Messages -----
CBTDriverError:uvbCbtSnapshotCreationStarted:: 20001002 <CBT_CTL_DUPLICATE_SNAPSHOT_CREATE> +
Due to previous error, Unitrends agent is not able to use the Hyper-V CBT filter driver during backup job for VM {01A920EF-73DA-49C8-90C3-76D1F951E065}: all files will be backed up as full not change blocks.+
----- End Error Messages ----
The work around for CBT snapshot issues is to remove the VM from tracking and take another full backup.
To remove a Hyper-V VM from CBT tracking perform the following:
1. Open command prompt as an Administrator
2.Run the command to obtain the <VMId>
powershell Get-VM <Name> | format-list VMID
3.Using the <VMId>, run the command to remove VM from CBT tracking
C:\unicbt\bin\uvbsimulator.exe remove <VMId>
4. Schedule or Run a Hyper-V full backup of the affected VM