Bearded dragon refusing to eat for a month and more

Hi all, my male bearded dragon hasn't been refusing to eat anything for the past month and a half. I've tried to force feed him and it has been unsuccessful as he keeps spitting out the food with his tongue, only a small amount of the food I force him to eat makes it in. I've had him for around 2.5 years, and he came to me as a an old juvenile? (I'm guessing because the previous owner seem to have gotten him from another source).

Tank set up:

100 gallon tank
basking zone 98F
cool zone 82F
10.0 UVB coiled lamp (changed every 8 months)
no substrates used, only a mat

Diet: collard greens, bok choy, green kale, bell peppers, steamed butternut squash
Treats: Apples, blueberries, mangoes
Insects: crickets and hornworms (treats)
Repashy: veggie burger, bearded dragon buffet

Crickets are gutloaded with repashy superload and dusted with multical powder and fed approximately 3 times a week. Salad is offered fresh everyday (also dusted every other day) in his bowl. He has been drinking water normally.

I took him to the vet a week ago for a fecal examination and body check, but they didn't find anything unusual and the fecal results came in negative (no parasites of any sort). This is really worrying because I don't know what I can do to make him eat. He's been acting like he normally does (no signs of lethargy) but has noticeable weight loss. He's also been passing stool as usual but obviously there was less each time because he wasn't ingesting much. I've also been giving him warm baths each day to make sure he stays fully hydrated. I've attached an image of his stool below.

If any of you have experienced something similar before please help me out hear, I'm really stressed about my beardies health.

Hi. You definitely want to get rid of the coil uvb and replace it with a reptisun 10.0t5 long tube. Can you post a picture of the set up and the boy?

Hello,

Do you have any pictures of your dragon for us, along with your tank setup so we can see
the physical condition of him?
Your 100 gallon tank sounds splendid, what a lucky little man you have.
I have a feeling he just needs a better UVB light. As suggested, the Reptisun 10 T5 or the
Arcadia D3 12% or 14% T5 either one are very good. They are tube bulbs & are higher
UVB output so they do last quite awhile.
With such a large enclosure, I would also recommend using a MVB too, such as the Solar Glo,
Powersun, or the Arcadia D3. You could also get a Megaray too, then mount the T5 a bit further
away concentrated on one end so that 1/3rd of the other end of the tank is without UVB & a
lower lit area.
What type of thermometer are you using, a stick on type, a digital probe or a temp gun?

Let us know how he is doing.
Tracie