I have a hen that lays me one of those about twice a week. I have no ideal for sure just lots of guess, but the one thing that sticks in my mind is she is old. ???? is your hen older? It was suggested to me once that we were giving too much calcium. but don't have to put any out, they get plenty in the feed plus they free rang all the time. I put some out in the winter just in case but in the past 3 years I have refiled it maybe twice, I still have the same little bad I started with. Sorry I couldn't help, just wanted you to know you weren't the only one.