em, Lumia 950XL and all x50 series are not interop unlocked yet .Tried with a friend who has 950 and same thing happened. It seems like Microsoft found a way to restrict registry access even if you're interop unlocked.
The NDTKSvc of these phones have a white list (same as the new version of NDTKSVC on older phones) but you can simply restore NDTKSvc on old phones but you can't do that on new phones (because of different signs) ,
but surely we could finally find a way to make these devices unlocked too .