I just experienced this for the first time today.
I noticed yesterday that my hen that lays green eggs for me was in the box for a fairly long time yesterday and when she did finally lay, there was a little blood on the shell. I looked it up on the forum and read a little bit. She's still new at laying, so I didn't really think anything of it... Yesterday was her 10th egg, it was 53 grams. And I thought, well, maybe she's still adjusting to laying and is having a little bit of trouble with these latest, bigger eggs.
She was due to lay again today, and then take tomorrow off.
She again spent a long time in the nest box today, and I noticed that the top of her comb was nearly white. So I gave her a gentle pat closed the lid on the egg box and let her be. An hour later, I went to check on her... she wasn't in the box anymore, but there was a big shell-less egg with a partial white membrane. The yolk was missing. I don't know if she ate it or if another hen found it and ate it or what...
I cleaned out the box and tossed the mess out into the woods and then went to check up on her.
I found her by the waterer... her comb was a whitish blue and she didn't run away from me when I approached her like she usually does. She didn't squat either... she just kind of stood there.
So... I picked her up and saw that her bum was a bit of a mess... I carried her inside the house.
My biggest fear was that she had some egg shell still up in her... so... I drew her a warm bath and cleaned her up. She seemed to appreciate the attention. After a little further inspection, I no longer believed there were egg shells in her. So, I wrapped her in a towel and held her in my lap for a while. I massaged her comb a bit too as the color seemed to be returning again.
It was warm enough today, so I put her back out with the others when she was reasonably dry. I check on her an hour later and she seemed to be doing alright and have good color still... She was eating right before bedtime too.
I keep everything about my hens laying habits recorded on a spreadsheet. She usually lays for three days, and then takes a day off... roughly 27 hours between eggs. Her last two eggs were 3-5 grams larger than the four before and she laid her shell-less one 23 hours after yesterday's, a.k.a. 4 hours sooner than expected. So, I hope this was just an anomaly.
Poor lady.