Not unheard of, but 10 month old chickens should not be molting. How much corn are you giving with the layer feed? Corn will really water down your protein % & depending on how long you have been giving it to them, it could have just hit them now. I give a cup or two of scratch to my 11 chickens each day that is 9% protein and they still lay pretty well. Some feeds are better than others also. Hope you figure it out.