Could you have a snake? Even if you don't see it any predators will disrupt the laying for a few days. I maje rice with raisins or oatmeal and raisins aling with their usual feed, also are you giving them calcium? I use food grade diatomaceous earth, mix some in the rice or oatmeal.
I have not seen all the answers but I read pine chips can be toxic and have to be used in a well ventilated coop. Maybe when the chips got hot it released the fumes from the chips. We used a dog crate with brown paper liner and hay. Don't give up!
