Take this for what it is, as it's not necessarily the problem.
You're attempting to use hardware passthrough with a CPU that was released in 2012. Hardware passthrough is highly dependent upon proper support of IOMMU from the cpu, chipset, and BIOS.
Historically, this support while being technically available on consumer level products has been present, it has not worked very well until the later generations of cpus / chipsets. This is especially true with regards to AMD instead of Intel.
No software can overcome hardware limitations, and unRaid is no different in that respect.
What you need to do is see if the restarts happen without the VM service even being enabled. If they don't, then the passthrough support from AMD on that generation is entirely to blame. If they do continue, then it's something else.