Signing the drivers with Microsoft costs about 8000 Euros, but our original drivers which now do not install are signed by Microsoft and still they do not work.
I think it is very likely that Microsoft messed up something in their latest Windows update is why this is not working now, just like how they did with OpenGL some time ago.
But again, it should work with Secure boot option in the BIOS off and the signature enforcement in Windows off, I mean any drivers should install that way no matter if they are signed at all or not...