Backyard Fowl Keepers

If nothing else seems to work, you might want to do a round of deworming. Internal parasites can sometimes cause poor feather regrowth since they steal nutrients from the bird. A fecal test from a vet can confirm if that's the issue.

Have you checked their legs and feet for scaly leg mites? Sometimes if chickens have an ongoing mite infestation, it can spread to their legs, making them more uncomfortable and possibly leading to further stress-related feather loss.

Since your hens are active and eating well, it's possible they are just going through a rough molt. Some chickens molt harder than others, and irritated skin isn't uncommon. Keep up with the high-protein diet and maybe add some electrolytes to support them.

My flock went through something similar, and it turned out to be mild chronic stress from a nearby predator (a raccoon hanging around at night). Any chance something is disturbing them at night and causing stress-related feather loss?