Ok, hold the phone. I believe you just answered that question yourself if I understand correctly that he only has ONE good hide.

Snakes will readily choose security over warmth. If both hides are not identical, then the snake will see one as more secure and stay there 99% of the time.
Plus, if you're keeping him in a too-big tank with only one hide and a log (which aren't good hides because they don't surround the snake) then he may also be stressed out, and a case of scale rot isn't helping.

Do what you can to get the tank up to standards, as it were, with two identical hides, cover for the back and sides of the tank, and foil treatment for the screen. I'm sure you already know this, but keep him on paper towels only while treating him.