I have a hen who is laying an egg with no shell. There is only the membrane surrounding the egg. Obviously, I've only found two of these eggs, since I'm sure the others are broken as soon as another hen scrambles into the next to lay. I've added oyster shell to their diet. I'be put probiotic in the water. I've also added an egg booster to their feed - still no shell after three months. Has this happened to anyone else?