Ask the Chess.com CEO:
http://www.chess.com/forum/view/community/erik-from-chess-com-here-ask-me-almost-anything
In the discussions so far, some guy reported the same problem to CEO Erik and he seemed surprised, asking the person to email the details.
Hi I am new to chess app and like it. I was playing a game last night and lost connection. I closed the app and reopened but it did not take me back to my game. It was at the most 45 seconds. I need to know in future how to rejoin my game. Thanks