Q: I upgraded the BIOS/UEFI on a Hyper-V host, and now virtual machines that had a saved state won't start because it says a process-specific feature isn't supported; what can I do?
A: The most likely cause for this if you updated the BIOS/UEFI on your machine and your saved state virtual machines no longer start, giving you the following error message
The virtual machine '<VM Name>' is using processor-specific features not supported on physical computer '<Hyper-V Host>'. To allow for migration of this virtual machine to physical computers with different processors, modify the virtual machine settings to limit the processor features used by the virtual machine.
is that during the upgrade, a feature of the processor was disabled. Go back into your BIOS/UEFI and turn on the feature(s) that were disabled.