I'm also interested in what you get for an answer here. I've been having a similar problem. It started about 7-8 months ago. I have 6 chickens affected (all of them). When it started, I thought it was their first molt. But, the problem never went away.
It's like their feather fell out like a molt, but then they don't come back in right. Those feathers that didn't fall out look like the hair of the feather (barbules) are being stripped, leaving only the barbs on the shafts and looking very scanty.
I've looked them over for lice several times and didn't find that to be the issue. I keep DE in the coop -- to attack the possible mites. I feed them Feather Fixer and Hearty Hen (both 18% protein), and it doesn't help either. I haven't tried anything else yet.
They are not broody (well, not all of them, and not all of the time). I can't figure it out. Must be a parasite of some sort, but what?
I thought about worming them, but honestly, I live in AZ where it is hot and dry. Worms have never been a problem...and my research on that doesn't imply feather loss as a symptom anyway.
Help me Obi-Wan, you're my only hope!
Here are pics of the motley crew. They look AWFUL!