The window goes black without UI, and the music keeps playing. And after few minutes, you get the message saying " connection to server timed out".

It's frustrating to me, as it happens so often. And there is no way to cancel the matchmaking. I have to wait few minutes till the message pop up, or alt F4 the game.

Add a shortcut to cancel matchmaking would be better.

Yep same is happening to me aswell all of a sudden. Join server black screen and pop-up message "Connection to server timed out"
Not messed with PC internet settings or anything,the error started to day.

They can't fix the brightness bug since release, I doubt they can fix the black screen bug.