"Storage_interface.Does_not_exist" on offline VM cross-pool copy

I try to copy a VM that's shut down from one to another host (error occurs both via XenCenter right-click>Copy VM and with "xe vm-migrate ... copy=true")

With several VMs that have around 250GB drives each, it works flawlessly

With one VM that has around 1.1TB drives (200+900GB), after ~40 minutes, the operation fails with "Storage_interface.Does_not_exist(_)" error. On the destination host, 3 VDIs only visible via "xe vdi-list" are created, named and sized like the 900GB drive of the VM I'm trying to copy. One of them appears only to be allocated, two of them go within the "used" space.

SR Space before migration start:
766.1 GB used of 6663.2 GB total (766.5 GB allocated)

SR Space after failed migration:
2569.6 GB used of 6663.2 GB total (3466.5 GB allocated)

So there should actually be plenty space for the operation, yet it fails and I'm not sure what the error message wants to tell me.

I'll be happy to provide a Server Status Report if someone gives me an upload link.