My BPRs went through this and I was able to resolve it---
Shell-less eggs. I think that there can be a lot of causes for the chicken to loose the ability to create a good shell.
Do they get enough calcium? Free choice oyster shell in a container is good, and crushing the shells of the eggs you use and feeding them back to your flock is good. My chooks prefer egg shells to oyster shells BTW.
Apple Cider vinegar in their water (1TBSP per 1gallon of water) - helps the chicken's digestive system absorb nutrients -- including calcium, it has to do with the pH factor.
Vitamin D3 helps the hen with egg shell production too. I bought a bottle of tablets at WalMart and crushed up one. put it in with some feed and the contents of the shell-less egg (she was making membranes but no shell) - so vitamin D3, and more protein and good quality layer feed with the most calcium of the available feeds, They tended to gobble that down.
Old age, and other factors can interfere with shell production if you think your hens may be approaching the end of their laying period.
You may want to search on shell problems or eggs without shells in the search at the top. This cut and paste is from another post - but this question gets asked so often that I keep this on my 'charts and quotes' page. so I just cut and paste. (efficient or Laaaaaazzzzy?)
LOL.
I pulverized my eggshells in food processor, mixed with powder from crushed D3 tablet, then feed and egg. I just about always put cider vinegar in their water. HTH
Ditto here......I save their egg shells, bake them dry in the oven, crush them and add them to their feed. I also offer oyster shells, but none of my chickens even touch those. I think they must be getting enough calcuim, so they do not need the oyster shells. I add ACV to their drinking water too......~Beulah