I forgot to tick a box somewhere in the last few builds, and that box turned on Steam Achievements....
The newest patch should be up within a few minutes of me posting this.
Sorry for any trouble this caused!
Source: Steam Community (opens in a new tab)
Build and release context
Steam update times within 24 hours of this post. Matching dates do not confirm which build it describes.
Build 5257384 · public branch
Steam updated · First observed