Okay I found out the hen that is laying the eggs with soft shells is my youngest hen (who I didn't think was laying eggs yet). Apparently she is laying two eggs at the same time, and they both are extremely soft. I had no clue a hen could lay two eggs. She has done this twice now. I've added the crushed oyster shells, and have seen all the hens pecking at them. Thank you for all your input. I'm hoping it gets better soon.
That can happen when they don't have enough calcium, the first egg sits too long, then the next one sits behind it. Try the oral calcium pills, I bet that will fix her.
Just want to give you all an update. Since I started feeding them crushed oyster shells, we haven't had any issues with soft shells. Thank you all for your advice.
A Canadian feed company study showed that the hens picked up the oyster shell when the egg entered the shell gland, where it remains for about 18 hours.
The large particle size works better than the calcium in the feed because it stays in the upper digestive tract longer and makes contact with the calcium absorption sites in the intestines during the night when the hen is sleeping (and building an egg shell).