Hyper-V in Windows Server 2008 R2 and later, around spring 2014, introduced a HyperV backup mechanism where Hyper-V creates a hidden internal checkpoint when a Hyper-V backup is initiated. Shortly after the server backup software goes into its prep phase, this checkpoint is deleted and merged automatically while the backup proceeds. See below:
If the host server or cluster node fails exactly during that short timespan, the checkpoint may get stuck. The Hyper-V Manager screen won’t allow you to delete it either.
How to Delete Hyper-V Backup Checkpoints that are Stuck
In order to delete these kinds of internal checkpoints / snapshots, use the PowerShell command:
Get-VMSnapshot -VMName-ComputerName | Remove-VMSnapshot
Remove-VMSnapshot -VMName "adaudit" -name "adaudit - Backup - (12/19/2015 - 11:15:27 PM)"
The above command will take care of this issue and the backup snapshot for you.
There is also a hotfix available by Microsoft at https://support.microsoft.com/en-us/kb/2964439 titled “Hyper-V virtual machine backup leaves the VM in a locked state”; however, the above PowerShell command will do just fine without the hotfix.