You got disconnected.
https://support.chess.com/customer/en/portal/articles/1444918-my-internet-connection-is-fine---why-am-i-getting-disconnects-
https://www.chess.com/blog/News/how-to-adjust-your-live-chess-connection
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I was waiting for the last game to start in my tournament. It never started and I went to my stats page and it showed I abandoned the game. Has the happened to anyone else? What could I have done to cause this? All I did was wait for round 5 and it never came. This also happen to me a few weeks ago.