So something strange happened when I started the game earlier: I was hit with a window that said I only had one hour of free gameplay left and that I need to buy the full version.

...I'm sorry, what? :/

I bought this game months ago during a Steam sale and I've spent dozens of hours playing it (I'm up to level 106 in endless mode). If I lose access to a game I purchased because it suddenly thinks I'm playing a demo I'm going to be very ticked off.

So any ideas as to what is this all about? Is this anything I should be concerned with? Or at the very least, is this happening to anyone else? Thanks.