Another 6 last night, including a small white egg, which I think is from my banty hen that is still raising those 4 chicks (the biggest of which is almost as big as she is). That's 8 confirmed layers, maybe more.
Last night when I was out there to lock them up I noticed one of my newest roosters was down on the floor of the coop, with the same symptoms as the previous half a dozen or so chickens that have died. I didn't see him there this morning so I don't know if he got better or if he crawled outside in the dark. This is starting to eat at me and I think I'm going to have to break down and start looking for answers over on the chicken board, unless you guys have any ideas.
In every case, it comes on very suddenly. I find a chicken laying on the ground of the coop. You can tell that they aren't right because they are kind of laying on their side, not sitting like a normal chicken. They don't seem to be in pain or overly distressed. It's like a partial paralysis or something. They can't get on their feet to walk, but they will live for a couple days before I give up and put them out of their misery. I just don't know what the problem is. It seems like if it was a disease it would affect more chickens than just 1 every 6-8 weeks. They show no other signs of illness or getting picked on or anything. Very bizarre.