I must admit I've never fully understood the night time drop for leopard geckos.
In the wild they hide during the day and come out at dusk until dawn, as they do in captivity. For warmth, they will lay on heated rocks (from the sun during the day) that hold their heat for several hours.
It stands to reason that during the day, hiding away, they'd actually be colder than at night. And seeing as heat is an active ingredient to their digestion and they eat at night, why would you out the temperature down at that pivotal moment.
I'm not saying don't as it's obviously a widely believed aspect of leopard gecko care but personally I do not dim the heat at night. My vivarium has a very good thermal gradient and the heating in the house goes off at night knocking down the cold half a couple of degrees should my girl fancy cooling down.
I would say in this case, if you're going to drop the temps for night time 22c is a bit low, at the least the lowest you should ever go. Maybe up the temp and see if it helps.
As others have said, he could still be settling in but you shouldn't hold your hopes on that too long. Even when the enclosure is new Leo's generally take food quite well.
If you have any concerns, doubts or worries about your animals health always consult a qualified veterinarian (with the necessary experience).
Nobody can properly diagnose an animal based on descriptions and photos. Especially when those animals, such as reptiles, have a small list of visible symptoms than can be found across a large range of problems.
Always see a vet. Don't let strangers on the internet make you do something you'll regret. They won't take responsibility.