Sorry, I think it's a bug with the itch app, not with the game itself. I had both the demo and the full game installed, the demo updated properly but the full game didn't, so I uninstalled the demo in order to get the update option for the full game. Apparently running the update removed the full game and installed the updated demo instead, and the game's still listed as purchased under my account but the only version itch will let me download through the app is the demo.
So that sucks, but that's the app's fault, not the update. I'll download and install it outside the app and that should fix things.