Hello,
Is there anything sharp that he could be rubbing up against perhaps?
Have you measured the temperatures of the tiles to be sure there aren't any spots that are
warmer than other spots?
If he climbs up & down a rock, etc sometimes they can scrape up their scales to some extent,
if they are repetitive at the motion.
It could be possible bites of some type. What insects do you feed him & do you feed him in
his tank?
For now, you can get some raw, unpasteurized honey to put on those areas but make sure
there aren't any insects in the tank that would be attracted to the honey.
Tracie