Change those things that need changed, get an exact temp in all the various places, especially on the surface of the glass over the heat pad and also how are you checking the humidity? I know you said digital, but I just wondered which type?

Once all of that is switched around, I would definitely try a rat crawler. Are you feeding him in the cage without disturbing him? I.E. placing the prey in and leaving him alone for a while? A crawler should be harmless to him so leaving it in for him to smell and find it should not be dangerous(live adult mice can be a danger though).