It will take some time to find out cause for this problem. Check topic on forum after day or two.
For now you can try to reset settings by holding keys R and P for 5+ seconds on login screen (just click outside input fields).
Hey!
So there was this guy who was talking about the clan tag right. I tried that and it actually worked for me! I changed my clan tag quickly and closed the game before it closed itself. Now it works perfectly fine after i restarted it again.
