I’ve noticed couple of times the following use case. The use case has happened on slow connections whenever I travel (I try to play a game or two when I have a longer flight or bus/train ride).
I start a challenge. I get the screen that waiting for somebody to accept. Nobody accepts and I’m doing my email at the same time. At one point I read an email that a game has started and also stopped. I check my browser and it still says waiting for opponent.
Once I refresh the page I see that I actually don’t have a challenge up anymore but a game has started and ended (opponent gave up waiting for me and cancelled the game).
Now whenever I start a challenge I also try to spot the challenge behind the Waiting for opponent overlay in the listing because one time the game started so quickly that I still saw the Waiting for opponent overlay but when I opened another tab I was able to navigate to my already started game.