My 2 Amerucaunas are producing eggs with circular bumps of shell material on the surface. Some are tiny and granular and come off if you lightly scrub them, others are fused into the shell. They have been laying for the last 3 months, and the eggs had a smooth surface for the first two months. I've also noticed the eggs are significantly lighter in color than previously. Laying frequency seems to be the same. They are fed layer ration with plenty of free range time in the back yard. I had free choice oyster shell out, thought it might be the problem, and let it go empty, but it has had no effect. My other various breeds hens are having normal eggs. Any explanations?