I got a similar problem today, so i write it down in case it helps. I played in ranked draft pick mode, solo que, without any premades. I was in pick and ban phase. The banning phase ended, i picked my champion and waited. One of the enemies tried to pick master yi, but it seemed like he didn't lock in. Then the game sort of crashed and everyone waited. I texted to my teammates just to ask if they had the same problem and they all said they did.
Then the message - dialog box said that all my teammates left the game, all at the same time. I was the only one who stayed in the game. So, i closed the game and tried to reconnect. My first reconnection was a failure, as it said that i had left a game and needed to reconnect, but instead of the loading screen with champions in frames, my screen went black.
Then i used Ctrl- Alt- Del and i tried to reconnect again. This time it worked. When i got back everyone was at level 6 and they said they never left, even though they had the same problem as i did. I told them my screen said they left, all at the same second...
In the end we won, the game is counted in lolking, i raised my lp, but i got a penalty of 10 mins for being afk.
Later on, me and my friends encountered similar problems (e.g. double-click on the icon of the game opens two games, u try to close the one and they both close - after the match has ended u can't see the stats and when u try to close the game it stucks). Even more disturbing is the fact that lolking hasn't counted one game that i played earlier in the morning.
Finally I repaired the game (main screen - question mark icon) and until now it works fine. Many players are afk due to such bags and i think it has something to do with the new patch.