The male may not be able to cover all of the hens. That is a lot for a button to cover. Another thought I had - are any of them pearl? Pearl is double dominant fatal, so if you breed pearl x pearl you will automatically have a lower hatch rate.
I keep my buttons in a variety of setups, depending on the space of the cage and the personality of the birds. They should have one square foot or more per bird. Since you have some hens with feathers missing, it looks like you have an overzealous male, or possibly you only have 2 hens. Can you...