I agree, it doesn't look like molting, but the season will soon be here. Mine seem to molt when it is cold out. Go figure.
If it is mites or lice, you will see them around the perimeter of that area, on the head & under the wings and under the tail too. Mites will look black. As for lice, you will see the egg cases at the bottom of feather shafts. Lice will be very busy trying to hide in the feathers. They are fast. Funny thing is, I think that all your birds should be showing these signs if they are in close proximity. Even if you find some, don't assume your problem is solved. You could be having more problems than just bugs.
I would still go with the pecking idea, especially since it is your layers only. I had layers that would either go for the neck or tail area. One of those birds still looks like a naked neck. The feathers didn't grow back on her. She looks like your picture, just a little worse yet, but now healed.
I removed the picked on ones for healing (the picking got bad fast) and treated wounds with honey, which is a great healer. I watched for the perpetrator & removed the most obvious two. I still watched for trouble in the rest. I only put them all back together after I added a "law & order chicken" (2 paragraphs down).
Layers often will go after each other and when they do, they are vicious. I don't know how Stop Peck would really help since it appears to be red. Chickens love pecking red (and new) things. I have read that special applications (like Stop Peck) don't always work. Blood & feathers are full of protein, and they may be letting you know that they need more protein. They will keep at it until they kill each other.
If they are pecking, I would introduce a larger mature, confident and no-nonsense rooster or large no-nonsense hen to introduce order (both worked for me with some cannibalistic hens). Just dump it in there. I used jersey giants in both cases (because I have them) and they worked well. Watch the newcomer closely for at least the first week. Watch for any sign of getting picked on. See if they are standing up to the purpetrators successfully. Mine both did well at restoring order. I haven't had an issue since.
I would also give some extra protein (free choice). I know some people who give meat, under supervision, twice a week.
Introducing some "toys" might help with boredom. Winter can get long if you are always cooped up. No pun intended initially.
How is their space? Could it be that they need more?
I would troubleshoot all of the things above. Good luck, and let me know (on here or by PM) how things are going. Finding this sort of thing can be very offsetting.
I can also recommend a good Canadian poultry forum where you can ask questions if you would like to ask on there too. Just let me know. They have been a great help to me over the years.