I think I know what is causing this and how to prevent it. A lot of people are having this problem. The screen is either white, black, or you can't select champions during champion select regardless of what mode you areplaying. It has happened for me in ranked, normal, and ARAM. This happens when your PVP.net client disconnects from the server while finding a match. If you accept a match around this time, there is a good chance that you will get this bug.
To prevent it, if the disconnected from PVP.net notification is going on and off, I do not try to find a match or I quit the finding a match until it stops.
I have attached a picture of the message. Whenever it happens, it flashes on and off repeatedly. This means that the client disconnects and reconnects rapidly. It happens for about 10 seconds or so. After it stops, I can find a match and get to champ select without any problems. This normally happens right after I log in.
Basically, if you wait a little before trying to find a match after you log in, you shouldn't have the problem.
Не съм в нас та да ти го обясня по подробно , опитай с това. А и тва за прикрепената снимка е снимано тва горе в ляво дето като има някъв проблем те уведомява , та да не те притеснява че няма снимка
