Aahzathoth: Thanks, I'd be happy for an update :)
While we're on the topic - where the heck are we supposed to create an account? I don't want to install Galaxy just for this, and however stupid that sounds, I can't manage to find anywhere the ProNet website. One thing googles up, but it doesn't seem to have anything to do with the game.
It seemed to fix the problem for me. I was able to click continue, and after that the game asked me to rate the level. I doubt that's a coincidence. However, I turned off my wi-fi to test if it would happen again in the second level, and it actually didn't, it just skipped over the level rating screen. I wonder if signing in at least once fixes the issue. I should note I uninstalled and reinstalled the game as well, but all of the app data and settings were the same, so I doubt that's related (might still be worth a try for others though).
One other thing is that the game comes with an offline mode, which is easy to miss if you just launch the game from a desktop shortcut. It wasn't there in early access if I remember right. The bug might not affect that mode.
I think making an account requires Galaxy for the GOG version, though I'm not 100% certain of that.