My own experience moving my mare when she was laid up with a broken leg was pretty disastrous. I thought I was doing the right thing by moving her to a full-service barn where someone could look after her all the time, rather than me just stopping by morning and evening. But she hated it, got super-stressed, and ended up in an equine hospital with colic within a week. After a week at the clinic, I moved her back to her previous not-so-fancy barn (which fortunately I could) and her long recovery was pretty uneventful from then on.
I don’t know what your situation is, but if none of the suggestions from other posts help, maybe you could find another barn more like his old place? Are the stalls smaller than what he was used to? Or was he used to being able to see more of his neighbors? Maybe even moving him to a different stall at your current barn could help. If he is bored, perhaps a stall with more of a view? Or if he is stressed, a stall farther away from the ‘action’? Or maybe his neighbors are high strung and he needs more laid back buddies? Maybe he is not being fed as much hay as he was used to, or as frequently, or a different kind (alfalfa vs grass, for example)? Too much, or different, grain? Is his lay-up pasture more of a dry lot with nothing to eat, and he thinks you are going to feed him when bringing him in? Nothing like accidents waiting to happen bringing in horses when it’s feeding time in my experience.
That said, I think horses can truly like or dislike a place with accompanying behavioral issues. One of my horses used to break gates, stalls (basically everything imaginable), and be super spooky at other barns (without having any health issues). But since he moved years ago to where he is now he has just been Mr. Perfect. In his case, the fancier the barn, the more miserable (and hence ill-behaved) he was. Fancy places don’t necessarily make for what the horses consider excellent care and happy horses.
Sometimes, but not always, calming supplements can do wonders.
It sounds like you are doing the best you can, so don’t pull your hair out too much and don’t go it alone if you don’t have to. Having someone you trust (trainer, vet, friend) who can help you and your horse may make a big difference.
Anything forced and misunderstood can never be beautiful.
-Xenophon, 400 B.C.-