Vega 56 primary GPU passthorugh not correctly working after VM reboot (but displaying output)

Hey,

I have some weird behavior with unraid, when I try to pass through my primary GPU (AMD Radeon Vega 56). When I try to boot a VM (in my case a Ubuntu 20.04.2 live CD) with my primary GPU passed through, it binds and uses the GPU correctly on the first boot, but not on the second. While this sounds like the Vega reset bug, I am kind of unsure, since on the second boot, I get to the point where I can interact and select items from the GRUB bootloader (My prior experience with the reset bug when passing through was, that the GPU won't react at all). But after that, I only get to see the Tianocore Logo, instead of my GPU switching to the native monitor resolution and displaying the Ubuntu startup animation.

To summarize, I did the following:

1. I booted the Ubuntu VM with my primary GPU passed through (GPU bound to VM successfully)
2. I selected to boot the Live CD in the GRUB Bootloader and Ubuntu booted
3. After a short time, my GPU switched to the native resolution and booted into Ubuntu (like it would natively)
4. I rebooted the VM from inside Ubuntu (I also tried other approaches, which led to the same behavior)
5. After shutdown was completed and the VM booted again, I got to see the GRUB bootloader again
6. After selecting an item, the image (not the screen!) went black and the Tianocore logo was shown (At this point, nothing happens)

Unraid is configured to not bind the EFI-Framebuffer on boot and I pass the VGA Bios of my GPU to my VM.

Does anybody know a solution to this problem? Is this still related to the reset bug, or is this related to the GPU being the primary one?

Thanks in advance,

avocadoom