Seen plenty of soft shell eggs growing up and not sure if it was an illness or just lacking calcium but for the most part it cleared up after giving more calcium. The strangest thing I ever saw was a huge egg containing 5 yolks. My brother made the newspaper for that one since it was his chicken that laid it. That was crazy! I think we still have the newspaper clipping from the 70s on that somewhere.
Yeah, probably just lacking calcium. I guess the possible sickness is pretty rare.
5 yolks! Holy smokes! I think the record is 9. Haha. My quail gave me a 2 yolker yesterday! I get a few from the chickens as well, but 5, wooooweeee, that'd hurt! Poor things.