If the CPU is a different generation (for the OS to notice), you should also enable EVC mode. I came across this recently adding a few new hosts to the VDI cluster. The golden image vm also had be be exposed / booted to both CPU's. Otherwise when a user logged into a session that booted on a 3GHz host they would be prompted to reboot the system. Nothing is seen if the vm booted on the older host and was migrated to a new host, only if it booted directly on that host.
I would test a VM booting on the new host and see if you get this error. You may end up rolling through and rebooting each VM on the new host.