Righty given that he's so active even throughout the day ( they are nocturnal and are usually asleep at that time ) and given you're been conned into buying those stick on temp gauges which are unreliable at best ( for ambient temps ) and completely useless for giving the surface temps on warm and cool sides ...I'd guess that he's far too hot and simply trying to escape to a cooler area .
If they're recording 85F on the side of the tank the surface temps could be well over a 100 ...who l knows ..
As mentioned above , maybe the enclosure could be somewhat larger but just for the moment I'd unplug and even remove the lamp/s for starters and unplug the heat mat under the cool side and just keep the heat mat under the warm side for now. That will at least give him a cool area ... Next I'd get an affordable thermostat to regulate the heat mat under the warm side and get on eBay to buy a cheap digital temp gun for around 8 to 12 dollars .... Something like the one below - the make doesn't matter they're all reasonably accurate and reliable ..
Good luck !!
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