some vital vitamins/minerals. ANYTIME we have seen this in dragons we take in, its related to neurological/muscular problems and the base problem is usually not properly absorbing needed vitmains, mostly the B vitamins. I do not see any visual signs of early MBD in him, but its impossible to really tell over a computer looking at a picture
You can get a blood draw and check the Ca : Ph levels, but the first thing I would do is get a fecal and see if he has parasite or worms that are stealing the nutrients he needs to thrive....something is causing him to either not get them or not be able to absorb and use them. Nothing would be better than having a vet check him and give a professional opinion and he appears larrge enough for a safe blood draw.
The brewers yeast is a good call and what I would start out with whether he has parasites/worms or not. Crush and dissolve it in water or diluted gatorade and feed with a dropper or syringe to him, I would start with 1/4 tablet a day. They usually will drink strawberry-kiwi gatorade, if nothing else. The brewers yeast is water soluable, they will not overdose on it, excess will be passed out of the body.
Keep his dusting with Calcium with D3 going also and make sure he has a decent UVB source, it's not the time to play russian roulette with those that advise otherwise for their animals or yours. He's obviously got something serious going on and left unattended or leaving out something that is beneficial to them is not a good idea now.
Get a fecal, right temps, rich diet of greens, calcium supplements and minerals, AND UVB that you know is working and close enough to him. Leave any of those out and he's in trouble.
NOW, I will climb back in my hole and hide, leaving the forum to the professionals 
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