For me, after a significant amount of tweaking and trying, I finally found a combination that worked;
Machine Type: Q35 4.2
Bios: OVMF
Graphic ROM Bios (techpowerup download, hexedited to remove header)
And the following edits to the </features> section of the XML. ˜The highlighted lines are added in addition to the standard unRAID config;
<features><acpi/><apic/><hyperv><relaxed state='on'/><vapic state='on'/><spinlocks state='on' retries='8191'/><vendor_id state='on' value='1234567890ab'/></hyperv><kvm><hidden state='on'/></kvm><ioapic driver='kvm'/></features>