For you folks with hens sleeping in the nest boxes....
No guarantees that this is the problem in all cases, but worth looking into. Give then some light to find their way back up. It seems to me, at least in the ones I have dealt with so far, that with that tendency to get fussy over roosting spots comes the inevitable hen knocked off the roost. They don't see well in the dark and cant find their way back onto the bars. They sleep up high to feel safe, and lacking that will find something to sleep under, usually a nest box. If you find one in the nest box after dark, shine a light in the coop so she can see to find her way. If she goes up on her own, then try using a tap light or other cheap light in the coop while they sort out their differences. Once they've settled down after dark, you can turn it back off. Its usually about an hour after dark when I lock them up, so the light being on until then has solved that problem for now.
I did have a couple wandering around in the pen the other night after dark. I opened the coop and shined the light and up they went. Apparently they didn't get in before dark, which is weird. Maybe a couple were getting into it and they left the coop temporarily, only to not be able to get back in....
Anyway, try the light and see if that might be the issue. Good luck!