Hello @nikade.
I agree but this is my case.
Try to migrate a running VM: error 500
Try to migrate an halted VM: error 500.
Warm migrate: It's okay.
I don't understand myself the difference except it doesn't transfer the "VM" but recreate the VM and import the VDI, ( so , the same things ), but there may be a light difference. I don't know how the "warm migration" works under the hood