What you describe sounds almost exactly like my grow-out coop and what happens when I move chicks into it from the brooder, usually at about 5 weeks of age. I have a 4’ x 8’ elevated coop and an 8’ x 12’ run. I used to lock them in the coop section for about a week before I let them into the run but now I don’t bother. I just toss them into the run. If the coop were on the ground I think locking them in it for a week would make a difference but since it is elevated I don’t think it helps that much.
I think the problem is that it is elevated. I have two other coops on the ground and don’t have this problem with them. Whether they spend a week locked in the elevated coop or not, they never go into the coop to sleep at night to start with. They always huddle in a group, usually right under the door. I go down each night after it is dark enough for them to put themselves to bed and physically lock them in the coop. Sometimes they catch on pretty quickly, just once or twice, a couple of times it’s taken over three weeks of doing this, but eventually they all learn to go into the coop to sleep. I usually have groups of between 15 and 20 chicks. Normal is after two or three night a few start going in on their own and about a week later they all do, but not all groups are normal.
I lined the run wiring with ¼” hardware cloth in the area they like to sleep as added protection against a raccoon or such getting to them before I get down there to put them in the coop.
My brooder-raised chicks normally don’t start roosting until they are about 10 to 12 weeks old. Until then they normally sleep in a group in a corner or protected place. I have had some start at 5 weeks, some wait a lot longer than 12 weeks, but 10 to 12 is a good average. My last group of fifteen chicks started roosting at nine weeks.
How light is it in the coop? It doesn’t take much but they need to be able to see well enough to go to bed. My “window” for light is hardware cloth over vents up high, it works. Some people report it’s easier if they put a light inside the coop at bedtime so they can see better. I’ve never had to resort to that.
What you describe sounds perfectly normal to me. Other than just letting them go and taking the risk, which I don’t recommend, the only way I see is to go down after dark and lock them inside. Some people train the chicks to come to food and lure them in the coop before dark so they can lock them in there but I’ve never tried that. Not sure how that would work in your situation, but having them trained to come to you when you call or rattle a special “treats” container can be a good thing in other circumstances.
Welcome to the forum! Glad you joined.