Well not that I am aware of. Other than Sophia being ill back in the summer everyone is acting normally- of course I have older ladies who are slow and rickety, but everyone seems to have acting normally.Oh, yikes. Poor darlings. Has a respiratory infection gone through your flock that could’ve caused a shell gland issue?
Having said that it is migration times and I have seen ducks flying over and I know they can carry a virus chickens can get which causes brittle eggs. But I would think that something like that would go through the whole flock and cause all the eggs to be affected.
This morning I caught Topsy in the nestbox eating a brittle blue egg that broke in the box. Did she lay it? Maybe. I cleaned out the box and she was back in there when I left for breakfast.