I had the same problem almost year ago and there were some suggestions (click to see my topic). I wasn't able to figure out what happened. I wish you a better luck.

Maybe a demo for a game has vanished, because of owning the full version now?

Well, this is the weird thing: in the beginning, I had same thought! But the only demo of a complete title owned which I remember to have is Infinium Strike and it's still there, in hidden mode.

I've never heard that happen.

It happened to me once. But since it was a mistake/bug and I hadn't actually bought the game (well, the DLC) I'm not complaining.

Really? Stuff falling off the shelf happened... sometimes a lot (Dragonsphere, Fallout), but removed from the order history?? That's scary.

I hadn't actually placed that order, so I think it's understandable. It was the 1-dollar DLC for Thimbleweed Park. There was a promo that added it for free if you bought it during a certain period, but there was a bug/mistake and it was added to everybody who already owned the base game. I realized it because I saw a 0 € order in my order history (DLCs are not that visible in the library). After a couple of days the game was removed, as well as the order in the order history. In this case there was never an email confirmation. But as I said, it was never mine to begin with, so no complains.

when I go to my game library I see 422 but when I go to profile I see 421, not sure if it's normal but it's been there since the launch of the profile page. I still till this day wonder what game it is or not, not sure if its a demo that got removed or something?..

Never had anything removed from library. Have had games mysteriously end up "hidden" from shelf, but never removed.