We know some of you are experiencing an unknown DirectX bug that causes your game clients to crash and prevents you from reconnecting to existing games. The problem is related to a recent change performed in game.cfg file and we're currently working on a permanent fix. The patch is expected to be shipped later today.
The issue seems to be caused when the game resolution set in the game.cfg is unsupported by the monitor the PC is using. So most of the players affected by this problem are those using multiple machines to play League on.
In the meantime, there is an easy workaround to put the game in windowed or borderless mode. In order to do so, locate the game.cfg file in \Riot Games\League of Legends\Config, open the file, edit WindowMode=0 to WindowMode=1 and then save the game.cfg file.
Hopefully there won't be many of you who are affected by this issue.
**Update 04.05.2017**: We were unable to fix this problem last night. Our teams still work on a hotfix, but it has to be extensively tested before we commit it to a patch, as the issue affects all global shards, not only Europe. I will keep you updated regarding our progress.
**Update 05.05.2017**: Last night we have pushed game client patch that fixes the DirectX bug. Issue is resolved now, but let us know if you still encounter this problem while loading into your game.