Client does not react after a few tab-outs (during Champselect)

Mostly, I'm not having problems. Frequently I've encountered a bug, where i was not able to select a champion nor pick a summoner, when it was my turn. I heard the "ITS YOUR TURN" sound, but when i clicked onto the client - whitescreen.

3 Times in 6 Queues now. Of course I lost plenty of points.

What did i do before: I tabbed in and out often, just to check what is banned / picked and what is not. The ~10th time, no reactions. There was no error displayed.

Greets ra