When trying to migrate a VM storage to a local device or through iSCSI using Hyper-V Manager or PowerShell you could see this:
The only solution that works is to restart the Hyper-V management service.
Restart-Service -Name VMMS
Get-VM -ComputerName HV05 | Out-GridView -Title "Select one or more VMs to Live Migrate" -PassThru | Move-VMStorage -DestinationStoragePath "V:\VMs\"
I was moving the VM including the storage, and I lost the connectivity to the iSCSI storage, thus the VM storage migration failed. When I attempt to migrate the VM again, the storage migration failed with error 0x80070015.
Hope this helps!