there are 6 birds with 2 roosts 4 feet long set at 2 levels. one of the birds that is sitting out has been blind in one eye since hatch. She rarely roosts or climbs on things as is as I think her balance is affected. The other appears to be her "bed buddy" I don't know which one is driving thisHow big is your coop and how much roost space do they have? If there is a lot of squabbling or fighting over roost space the lower birds in the pecking order may be reluctant to go in. If there were issues with the buffs that came and went that could also be the root of the problem. Does your coop have plenty of windows/natural light? Many chickens do not like going into a dark, closed in coop.
If there is only one nest box you may need to add another. Although half the time they all want the same box anyway lol!
My coop is about a 4'cube with a nest box attached to one wall. I can add more roosts but they is plenty of room for them as is. All the birds get along well.