I have one chicken that lays eggs that always have this rough coating on the eggs. It's non uniform and doesn't cover the whole egg. I can scrape or wash it off, which I do. I used to get two of these every day, but now I only get one and whoever the 2nd chicken was who was laying them has moved on to laying regular eggs. Oddly, too, they used to be very dark brown, almost as brown as a marans but are getting lighter. They also were jumbo egg. Whoever was the 2nd chicken laying them now lays smaller and lighter eggs because all the rest of the eggs are smaller and lighter in color. We have 7 chickens and I often get 7 eggs. So I used to get 2 of these jumbo dark eggs with the coating, but now I only get 1 and it's lighter in color but still jumbo and with the coating. This photo is blurry but you can see the coating. It's whitish in color.