Every once in while a random patch of copper ore spawns right next to an airlock, blocking it. This usually seems to happen once a dupe has passed through it although I haven't actually seen it happen, only discovered it later as my dupes fall asleep while trapped in an area with little to no oxygen (and subsequently dying of suffocation)
It has happened multiple times on the airlock at the bottom left of my base by the coal generator, and the bottom center of my base by the path leading right and down to oil.
It was working just fine until very recently, they've gone through those doors hundreds of times without issue.
I can dig the patch as usual and then its fine for a few minutes.
Dupe goes through an airlock