In short, a known Steamworks bug is preventing me from uploading new builds of the game. I've been holding off on posting about it since I figured they'd get it fixed fairly soon, but it's been a number of days already and I have no idea how much longer this situation will go on for. As I said, Steam support know about it, apparently I'm not the only one who's having this problem, and at the moment the only guidance from them is to keep trying in the hopes that this time it magically doesn't fail. Of course, on my shitty internet, each upload attempt takes an hour. steamfacepalm Will post a proper game update when I manage to get the new build live.