That tank looks very open and not secure for a baby Ball. I keep my babies(5) in 15qt plastic tubs and they shed perfect, eat every week, and like to tell me to "Hiss Off..".

I would try bumping up the temps to 94/84(That's where I keep mine), and keep them steady with no fluctuations. Then, cover the sides and bottom of the tank with some 3/4" styrofoam insulation board. This will help keep it insulated against drafts and make him feel more secure. Also, you may want to fill the tank to the top with loosely crumpled newspaper and leave him completely(and I mean COMPLETELY) alone for a week. Only change his water and check for urates/feces, and check temps of course. You may also want to get smaller hides as those don't look very secure(a bit big). I use plastic or clay 4" pot saucers(sit under the planter pot to catch water). Knock or cut a hole in the side of two of them and use those instead.

I like to use the 4" saucers until they start to turtle them and carry them around the tub. Then they get 5-6" ones

After he settles in for a week with the newspaper balls, higher temps and insulated tank, offer him a small adult mouse. Make sure the room is dark, pre-scent for about 30 minutes to an hour, and then place the mouse on the opposite end of the enclosure. Then leave him alone for about 15-20 minutes. if he doesn't take it, take it out and wait until next week.

I have an '05 female who is only a mouse eater. She is only around 300g(thin but not skinny). She wouldn't eat consistently in a 28qt tub, so I moved her to a 15qt to see if the smaller space would help her feel more secure. She doesn't get handled but once per week to change her substrate. She might eat one mouse every 2-3 weeks... Turd. The other 7 Balls eat like it's going out of style and pound the mice until I stop offering(fatties..).

Try changing around the enclosure(or even switching to a tub until he eats consistently) and giving him a week. No handling... He should turn around for you, hopefully.