14 dead chicks found in coop!

[McChooky]

I think I found out the cause of the mass pile up, I hope this info helps others prevent similar issues in their flocks.
2 days before the pile up I turned off their night light, they didn't seem to have an issue with this at the time. There was pretty bad weather on the days leading up to the pile up, the nights were dark with no external lights.
On the night of the pile up, the weather cleared, this co-coincided with a very bright full moon that rose in the early morning.
I found there was a quirk in the shed design (which has now been changed) that would allow a shaft of light to illuminate a strip on the ground near where the dead chicks were found. I think that the bright full moon was at just the right angle in the early morning to cause this beam of light.
The chicks must have left their playpens and then funneled down into the area of the light and piled on top of each other.

I don't really understand how the chicks can actually smother each other to death without trying to move out of the pile but all I can think of was they were half asleep and the lack of oxygen caused them to have hypoxic feelings which are apparently likened to a confused/warm/drunk/dreamy sensation. This is apparently why hypoxia is dangerous to humans and animals as we don't detect the dangerous lack of oxygen until its too late. From my research pile-ups in chicks and pullets seem to often be reported when chicks are transitioned into dark environments and then experience a event causing a beam of light to illuminate a strip in their coop.

I kept the playpen in place for a couple more weeks, more and more chicks perched on the playpen but still didn't use their wooden perches. In the end it was getting pretty silly with the chicks piling into the playpen every night so I bit the bullet, built another perch, rounded the corners in the shed and took the playpen away. I expected the worst but all the chicks magically perched on the roosts that night and have been doing well since! I still keep a dim night light on in their coop, it seems to help them settle down.

Thanks everyone for your help and suggestions!

I've noticed they'll move to the opposite side of their coop when predators tried to get in and go back to their favorite roosting spot the next night.I keep a light on so they're never trapped in the dark. Having no corridors helps prevents funneling and smothering