This is not necessarily the case in your situation, but I had a hen die a couple weeks ago after laying 3 soft shell eggs in 3 days. I didnt know what caused it, but then this weekend one of my great egg layers (they are all just over a year old) laid a shelless egg. I thought she was eggbound, but turns out she was infested with worms. Yesterday before I knew she had worms I spent the day giving her water with acv in it, water with molasses in it to flush things out, and pedialyte. She drank and drank all of the things I gave her. I ended up giving her two warm mild soapy baths, one of them today, and she was finally able to push out the broken shell along with a whole mess of roundworms. She then popped out a rubbery egg. I am mentioning this to you because my chickens really had no symptoms until they were really far gone. I bought some wormer, and am worming the whole flock. So far the second chicken of mine that got sick is still alive and she's "talking" and eating again, so I'm hopeful she'll recover. Good luck.
