Weird, but you'd probably have a better idea of what happened if you were on the same tab for the entire game.
Whenever I play a live game, I stay on the same tab for the entire game; I don't even like switching tabs for music, so I listen to music from my flashdrive. I'm guessing when you left the tab, the game was aborted for a reason. You didn't lose on time and you didn't abandon the game, because those cases would have your game still show up in your game archive. What move were you approximately on? Maybe the game auto-aborted if you didn't make enough moves before switching tabs?
https://support.chess.com/en/articles/8593801-how-does-game-abandonment-work
I was winning a 30 minute chess game, clicked off the tab, and now it isn't showing on Chess.com. It is automatically taking me to one of my two daily games and doesn't show the 30 minute game anywhere. Very disappointing...