I’ve gotten the game to be a black screen with sound just now. given the specific circumstances, I haven’t tried to reproduce it yet.
Here’s what happened:
I finished a match, I was on the summary page after the match (where you can click ready, leave game or review char progression etc).
From here, I accepted an invite sent through steam.
The game was trying to join, but the match was full. It just told me the lobby is full and the screen remained black with the same sound effects as on the summary page.
I had to alt+F4 out of the game.