Show only ready to play games

You can get past these library filters by using the search box to find the game you want to install. The filters are ignored for this, and once its installed it will be "ready to play".

Maybe... it's in the hidden folder?

Did This happen today only? This is probably something to do with tuesday maintenance shenanigans. I once also lost a game when they did a maintenance update, then it got fixed the next day. Wait a day and see if it fixes itself.