In my experience, it is hereditary. I ran into this with LF wheatens early on. I helped them out of the shell. Contrary to what I had heard, I had nice, healthy chicks who grew into strong, healthy birds, who laid big, beautiful eggs. That chicks could not break out of. Faced with the prospect of performing c-sections on an increasing number of eggs for generations to come, I made the difficult decision to sell them all as layers, and lost a whole season in the process. That said, if that concrete egg was laid by the best bird I ever hatched, I'd probably break them out, toe punch them, avoid using the male offspring if at all possible, closely monitor the eggs from the female offspring and only keep the daughters with the best (unassisted) hatch rates. It depends on how bad you need that bird as a breeder.