Entire flock dead overnight....locked in coop, no sign of predators

[staceyj]

My heart goes out to you and your family on this tremendous loss.
I’d refrigerate a bird if you haven’t already disposed of them and call your extension agency tomorrow, or your state vet school and inquire about a necropsy to solve this puzzle.

 

[Cyprus]

Well from looking at their website, it appears that they sell a specific electrical unit and heat bulb for this coop.
I wonder if that has anything to do with it.

 

[Mosey2003]

I'm sorry you lost all your birds

They don't need heat lamps in the winter. They're fine even under 0 as long as they're dry, ventilated, and don't have a direct draft on their roost.

 

[Ghosty]

I'm so so sorry! 9 at once would be a predator or poison surely. Maybe the predator got in a scuffle with the roo first night and knocked over the heat lamp, then came back for the rest. I would definitely get rid of the heat lamp though.

I just lost 3 pullets this week. Found the third yesterday, she is barely breathing this morning. All went lethargic overnight, won't eat or drink or move. I started them on Corid and medicated chick feed.

 

[micstrachan]

@Megswdw, I so deeply sorry for your loss. Truly heartbreaking.

 

[ChickenCanoe]

All the aforementioned discussion is possible.
Another possibility is a weasel or mink which can squeeze into a one inch gap they can pry open. They leave no marks, kill everything in the building and leave them splayed all about. I've seen it more times than I care to remember.
Get a necropsy on one of the birds. I don't know what state your are in but here is a list of poultry labs.
https://www.aphis.usda.gov/animal_health/nahln/downloads/all_nahln_lab_list.pdf