You get involved in some interesting ones all right, Oli! I have to admit I don't follow a lot of the cases you post because they get complicated quickly.
Going from cold to hot they see much higher vibration but no change in detectable resonance… that supports the idea that the thermally-expanding rotor may be in an axial bind. When they inspected the bearing and didn't see any skidding... did they see anything to indicate the bearing was carrying axial load, like unusual wear/discoloration on the roller edges and race flanges? If not, what parts do they think are contacting axially to restrain the expansion?
The other thing that comes to mind is a rotor thermal bow. That doesn't readily explain the upper bearing temperature, but who knows maybe the angle misalignment of the cylindrical bearing during severe bow causes heating (it's a longshot, I know).