I'm having the same problem. Tried hiding the fact that it's a VM with the methods listed in this reddit thread:
https://www.reddit.com/r/VFIO/comments/5xzwp9/vac_authentication_error_on_windows10_guest_in/
FTR that meant:
adding <feature policy='disable' name='hypervisor'/> in the <cpu> tag
removing the whole<hyperv> tag from <features>
removing <timer name='hypervclock' present='yes'/> from <clock>
adding <kvm><hidden state='on'/></kvm> in <features>
and spoofing the bios vendor and mb manufacturer using https://libvirt.org/formatdomain.html#elementsSysinfo
Every time I make changes it works for an hour or so, but eventually VAC kicks me out.
I really don't want to dual boot, I'd have bought different (cheaper) hardware for that.