I have 3 R I Reds & i P B Rock, they will be 2 years old in June. Great egg production last year from all 4. this year the Barred in laying deformed and thin shelled eggs. Some are not hard shells but more like a thick membrane and are easily broken in the nest. Their diet has not changed, layena, oyster shell, and grit. They also free range the backyard daily for a few hours. What could be causing these bad eggs?