Chicken going to nesting box after dark?

[Sandwitch]

I'm not sure if this is an issue yet but the behavior was so odd it had me worried.

Basically tonight at around 10:30pm I went out to feed our horses so I stopped by the coop like normal to count chickens and noticed one was "missing". I checked the coop and found her sitting in a nesting box presumably laying an egg. I figured okay weird I will check on her later and see if she's okay. I also double checked with the family and an hour ago she had been up on the shelf with everyone around sunset. An hour or two after seeing her in the nesting box I came by again and checked and saw she was no longer in the nesting box and was making her way up to the shelf where everyone typically sleeps. So I went in to grab her egg and didn't find one. I'm a bit concerned that she may be having trouble laying an egg. I'm not really sure what to do if she is having trouble with that. I'm hoping this is me overreacting and that she's completely fine but I worry and this has been weird. I'm hoping that maybe since today was an oddly hot day and everyone's egg production was a bit off/delayed that maybe that's the issue and she'll be fine tomorrow.

 

[Shabby Chic-Hens]

I am sure that she is fine. In the morning, check to see if it feels like there is an egg.

 

[Sussex19]

See how she is in the morning.
A slight possibility is that she could be thinking about going broody.
If you have any more concerns about her being egg bound in the morning, get some calcium, plus D3 into her.
If you don't have any, you should be able to buy the tablets in any supermarket; they are normally sold in 600mg tablets, give a whole one of those. You can just pop the whole thing down her beak, and she will swallow it without any problems.
I like to have some on hand, and give a tablet as soon as I even think there could be a problem.