EDIT: I seem to have finally been able to fix the issue for good. Let me know if you're still having issues with the game starting. :)
Hey guys - I've finally gotten a way to reproduce the "won't start" issue with the new update. For some reason, the beta version of Steam and Rubber Ducky don't get along, so if you go to Settings -> Steam Beta Settings -> Opt out of Beta and restart Steam so you're not using the Steam beta, the game will run again!
I'll contact Steam and see if they can fix the issue on their end.