If I had to guess, I would say that the issue is that non-server versions of Windows don’t have access to all of the features of the Volume Shadow Copy Service (VSS) for Hyper-V. Due to this, certain files can’t be “snapshotted” during the backup.
If you check the logs of your backup, you will probably see something similar to this:
As far as I know, there is no way to “fix” this. For my part, I just live with the knowledge that if I need to restore any of my Hyper-V VMs, I will need to restore the files and then reassemble the VM manually.
Edit: After thinking on it for a moment, there is a “fix”, which is to use Windows Server instead of 10/11. For people like me, that is cost-prohibitive at the moment, and so I make due with this limitation.