Those coops are for about 8 chickens each, They may be over crowded. I have one (what is left after a bear rolled it around) I had 9 in it which was ok because at the time they were small and young. But I wouldn't put any more than that in them. It could be an over crowded issue
Sorry if I missed it. How big is your coop/run. How may birds do you have all together? Are they over crowded? This can cause the older on s to not allow the younger ones to get any food and become malnutrition. I agree though treating with corid won’t hurt. Extra food and water available...