Recent AMD cards have a reset bug. Vega is definitely affected. It is a hardware issue, so it would require a major firmware rework at a minimum on AMD’s part to fix, and they have not fixed even with the Radeon VII.
If you reboot/reset/turn off+ turn on the VM, you need to reboot the host before it will work. The issue is that the card does not reset properly without a full bare-metal system restart, which is fine normally, but is problematic in a VM.
This thread has some info-