It could be parasites such as fleas and such. Did you make sure he did not catch any ? Its possible even for indoor cats to get some.
Here is what I found:

Excessive licking of the lower belly fur in cats can be caused by both physical and psychological issues. It might be that your cat is struggling with parasites, allergies, or dry skin. Other reasons can be that your cat is bored or is facing stress and anxiety. However, contrary to popular opinion, licking off entire patches of fur isn’t typically related to a behavioral problem in felines, and it’s usually a sign of an underlying medical condition, such as parasites or a food allergy.

I make damn sure and give him good quality flea protection. It costs alot but he is worth it. I refuse to let those asshole parasites near to torment my baby! My house is insect free. I hate bugs.

Void, of course.

Unfortunately, his tenure as house cat predated pretty much all the currently accessible digital means of recording his existence, so he exists in blessed memory.

That cat was a dog. He would poop in the yard and just walk away, not covering it. He would come when you called him. Ran right up like a puppy. Big boy, not very smart. During a hurricane in 2004, we looked out the window and saw a cat walking down the sidewalk in 80 mph winds, like it was an ordinary day. Of course, it was Othello.

Good luck with your lad.

I tasted it myself, and YIKES, it was disgusting AND the taste stayed in my mouth for over an hour and it made EVERYTHING taste that way - I tossed the stuff, and eventually pup licked less and less..

Personally, can't recommend icky tasty (it ain't!) spray as course of action!!!

One of my cats did that, I changed him to Purina One Sensitive and he improved a lot, plus he stopped random barfing. Many cats skin issues are food allergies.

may be in order

Probably get a cortisol shot.

Well at least I get to visit my old snakey girl Kali,an 8ft. red tail boa girl I had to give away when I lost my house.

Mindy just loves her. Kali was calm and so sweet she loved being wrapped around me with her head hovering over my shoulder as I puttered around my kitchen in the morning watching me make coffee.. I still miss her.

She lives in a floor to ceiling enclosure now at my vet friend mindy's office and she goes home with her at to her snake room..

It wasn't clear what caused it the first place - could have been an allergy, or something else that caused itching - but the problem, the vet told me, is that the licking causes more irritation and itching, so they keep licking and the situation gets worse. So kitty got a shot of cortisone to make the itching stop, and this solved the problem. The fur grew back and he never did it again.

a vet visit just to rule out tummy troubles- ck anal area to be sure he can reach it and it's clean- otherwise not much to do -my male would tear at his tail hair periodically but was otherwise fine- we all have our stress habits- glad he's not smoking: :chuckle

I hope you work it out.

Personally, I would try a dose of Frontline or Advantage and see if it helps. It is easy to use and takes affect within a day or two.