I’ve had KVM.ignore_msrs=1 set for quite awhile as a kernel parameter – is this still a necessary thing to have when doing passthrough with Windows 10 guests? For some reason I think I saw something about some improvements with handling this somewhere, and I’m not sure if this is still something you want to configure globally.
You can always try turning it off. I think there was some changes in mid 2019, so if your version is newer then that, then hopefully it should work. I don’t have a link or remember the details anymore.