For about a day, buying DET-33 was apparently the hardest thing you could do in it. Steam was handing out all 15 milestone achievements to brand-new players before they'd fired a single shot, including Xenobiologist, which asks you to catalogue all 135 enemy types across every territory.
That one's on me. I typed each unlock threshold into Steam's "minimum" box instead of the "maximum" box, which as far as Steam is concerned means "you've already done it." A very generous difficulty setting, but not the one I meant to ship.
What changed
If an achievement disappears after this update, the game didn't eat it. You get to earn it for real now, and it'll mean a lot more when you do.
Thanks for reporting this to me!