Chickens prefer to be high, thinking maybe raise the roost? Is your roost roomy enough for all? Close off the nest box at night, opening in the morning.
My roost is above my "nest box" with a poop board under it However my current 4BO (24wks) choose to roost on the lowest roost which has not poop board under it. So I've been putting them up where I want them roosting at night for the past week It worked for my prior 4BO but these are being very stubborn.