Odd behavior when it gets dark

[Col1948]

Mine make their way in by themselves, I leave the coop door open, funny there is always a pantomime, one goes in then another, then another, one comes out, then another goes in, then another comes out.
This goes on for about 10 minutes or so till they are all in, then I quickly shut the door.
I have a hatch type door to it but I notice when I have the coop door shut and use the hatch they all hesitate and going in takes them a lot longer.
If you do put a light in, have it on a timer and not to bright a bulb, because when it does go off it a bright bulb will put them in complete darkness, where as a low light won't shock them too much.

Also do a check as the others have advised as well.

 

[Cyprus]

I would suspect first a red mite infestation.
Otherwise, I'm thinking that there may be something visiting them in the night that you don't know about.