I agree with coach 723 that it looks like feather picking. They are also at that age for their first big molt, and they tend to lose their tail feathers and large patches around the neck. Take care of any lice or mites if you find them, and feed them either a good layer feed if they are still laying, or you can put them on 20% protein Flock Raiser for some extra protein. Limit any corn or scratch grains (or do not give them at all,) since they do not have even have half the protein or the other nutrients for a balanced diet. Keep any droppings cleaned off with a quick soapy butt bath if necessary, to prevent flies from laying maggot larvae. It is common for some people to sell perfectly healthy hens at this age approaching a molt, since they will take a month or so off from laying eggs.
If any look lethargic or have frequent diarrhea or blood in their droppings, get some samples and have a vet check for worms and coccidiosis. I would think about worming them with Valbazen now anyway, since it kills most worms in poultry. Give 1/2 ml orally to each bird, and repeat it in 10 days. If any are 7-8 pounds you can give 3/4 ml. Good luck.