Bitter eggs??

[Galadrielstar]

I'm currently experiencing bitter eggs as well. I currently have 10 hens, all the same age, roughly 5. My search "older hens bitter eggs" brought me to your question. I'll see about some more research and post if I find anything.
Rhode Island's, black sex links, orpingtons, americanas - not sure if I can nail down butter egg to hen, but I'll try!