Okay, so I like making space itself a villain, but way in which you've implemented that leaves me with questions. Specifically, whether this is a basically organic creature that just lives in space and uses camouflage, or whether it's some sort of metaphysical embodiment of space itself, like a "vacuum elemental."
You seem to be trying to have it both ways, because you said it was a patch of space that became sentient, but then describe its attacks in a corporeal way. Specifically, "crushing mass" sounds like the opposite of space, since "space" is specifically the absence of matter.
By the same token, I want to know more about how it interacts with oxygen and how the oxygen is harmful to it, because that's something that would need to be described to the players. Oxygen can in fact be a deadly gas to organic things, and was an atmospheric poison to life on Earth at one stage of evolution, before most things came to depend on it instead. On the other hand, if it's more of a "living vacuum," then presumably it can't help but suck up the oxygen but becomes "less of a vacuum" in the process... maybe sucking up air and other things makes it smaller until it can "regenerate the vacuum".
The map and location descriptions are fine, the monster is cool despite needing to be more fleshed out, but the whole thing left me feeling a bit flat. It took a while to realize what it is, but I feel like this is almost more like a single, elaborate encounter than a full module. There's no complexity to the plot, no "transgression" (to use the TOMBS model) that provoked the monster's violence, nothing to explore, no real mystery to solve other than that the monster can possess people, no variability in the possible outcomes other than defeating it, dying, or running away. You just kinda show up on a mission, fight a monster, and go home (or not).
So if you were going to do more work on this, those are the avenues I'd suggest... flesh out the exact nature of the monster a bit more, and put it into a more interesting context with more moving parts.