Maybe he could be allergic to something in the pellets? Or getting too much of some vitamin in them? Just an idea to throw out there. I've read some birds can be allergic to things and that some just don't do well with pellets or certain brands.
I agree, a vet visit is in order to rule out any medical issues. :hug:
Ditto that!..One of the best things you can do to stop plucking is to give them lots of foraging opportunities and the space to explore and do it. Hiding their food and making them work for it for example. A busy beak doesn't have time to pluck. I feed very little food in bowls but rather put it in foraging toys so they need to find it and figure out how to get it before they can eat it.