Just went through this myself, so here is what I and the BYC community came up with:
1. Molting?
2. Less daylight and you're chickens are now adapting to it.
3. Egg thief?
4. Are they hiding or burying the eggs so you cannot find them?
5. Egg bound? Doubtful that ALL of them are egg bound, so like me, don't think that is the answer.
6. EGG EATER!
Egg eater was what my wife discovered when we found a half broken shell, I had been complaining about egg shells being cracked but not busted open, one or more of the chickens had been rolling eggs out of nesting boxes and burying them in the coop open area (actually kicked the shavings against the lip of the nesting boxes and using it as a ramp), and that there was yolk on a few eggs that I did recover.
We had been waiting till around 2 to 4 pm to let them all lay, but now (this past week) we are gathering the eggs early morning (7 to 9 am), doing a second and third check through out the day, and keeping golf balls in the nesting boxes to persuade them to stop the egg eating. We have been getting 6 to 8 eggs a day, which is closer to what we were getting (8 to 11 eggs daily) from our 11 pullets.
Hope that helps.
