Can they actually get to the food? I've seen weird issues where it looks like they ought to be able to eat but for some reason they can't path properly. Try picking up their food and placing it down again.

The limit is, I believe, 10 chickens within 10 metres Bear in mind they do move around, so I guess it might possible a few eggs got laid while all the other chickens were at one end of the pen? You may have to kill a couple more to make sure the average population density remains low enough to reliably lay eggs.

I just keep throwing eggs back towards the fire, (I have 2 fires going) then move 2 chickens away from the large gathering of chickens that I have sectioned off. I spam build signs to seperate them & guide them away from a mating pair. This keeps the eggs coming, and also groups more chickens together for mass culling & collecting.

For the breeding pair I typically go about at least 3 corewood logs (4M) long away from the main group, so they are not disturbed by population per/ area issue. Still testing it somewhat however. I've tamed heaps of boars before so assume this is similar in fashion to that a bit.

Anyway might be a bit of trial & error try a few things out, see what works & what won't.