In my current base, near central to everything, I'm getting polluted oxygen bubbles spawning up from nothing. No Morbs, no leftover polluted water bottles, there's nothing there. Décor can't find anything as debris either. There's some empty sandstone pipes, a few vents, some cots, and some portraits. Under the constructed tiles that it appears to be spawning from is my coal/CO2 setup, and there's no airlock even close to the point of spawning.
I'd attach the .sav but it appears you can't take that file type.
It was rotting food hiding in a base tile.
I have no idea how this happened in the first place, sorry.