If that still does not help try the below:
Do you have multiple avhdx or avhd files on the VMs? Do you see those? If so you will need to merge them through the Hyperv Console.
Please make sure to make backups of your system prior to doing anything. You should also think about doing a System Cleanup for unnecessary files and updates on the servers (If there is no space internal to the VM).
See how to merge Hyperv checkpoints: