If it hard freezes when executing the vfio bind script for the Radeon, its probable than the crash happens either when it gets unbinded from the radeon Driver, or attached to vfio-pci in a dirty state. I don't see it blacklisted anywhere, so try doing so so it doesn't get initialized and try again. If you're using only the GeForce for the host, you aren't missing anything by doing so.
Add this to the Kernel Parameters:
If that works, I'm curious why the behavior change with the new Kernel...