Hello, I am dealing with the exact same thing at the moment. First time having chickens:
6 month old hens with feather loss in the same spot. More serious on hens in the bottom of the pecking order. I don’t have cameras so I assumed it was feather pecking.
I bought no-pick spray, and I think it was working so I relaxed with it a bit. After a couple weeks without spray, I noticed it happening again so I just started re-applying every other night or so. Seems to be working?
No mites as far as I can tell, and there are some patchy pin feathers coming though. I’d recommend an anti-pick spray if you are still having this problem! I also bought a hen apron for the bottom hen, who was noticeably getting her bald spot pecked at by others.