@seanmcg182 's post might be the answer to the original question, two years late.
Your lspci -s 0000:05:00.0 -v at post 8 shows (rev ff) and !!! Unknown header type 7f, which is the same pair he had, and in his case it came from bifurcating the wrong PCIe port in the BIOS rather than from anything XCP-ng was doing.
He says the unknown header is what then produced the device or resource busy error on VM start, which is the error you opened with.
I don't know whether your board exposes bifurcation the way his X10DRH-CT does, so it might not transfer at all.
@kuznetcoff777 if that machine is still around, it'd be worth a look either way.
