I don’t see anything too terribley wrong with your setup, humidity is fine, they actually do quite well at higher humidity as long as you keep things clean. The size is fine at this age, usually when they are this small, you can keep them in something very small and it acts similar to a hide itself, ex: breeder racks never have hides in them and can be quite small tubs for new hatchlings and they do very well in these setups. The issue is having a gradient in such a small area can be challenging. What works well for me is keeping the ambient temp a touch on the cooler side, like 73-75 degrees and then the uth should only be on a small area at the far side of the enclosure at 90. They can regulate their temp then as long as the enclosure is large enough for them to fit on one side completely off the uth.

With all that said, I’m not entirely sure it’s your setup causing him not to eat unless the ambient is too hot which I didn’t see. But it could just be he is still stressed or just doesn’t like what has been offered enough to start feeding again. Do you know what it was eating previously? If your trying to feed f/t, you may just need to try a live hopper mouse. Sometimes they just need that movement to get them interested enough to strike and then they usually get back on track. Continue with live then for at least a few meals until it gets to a healthy weight and then you can try switching back to f/t.