After I click the Join Game button on the right side the screen goes black save for the "BETA" sticker in the top left and I hear the Main Menu music. Only ways out are closing and reopening the game or if you're in a party and get pulled into a match.
Black Screen When Joining A Server Through The Server Browser
A friend and I both had this same problem twice when playing yesterday.
Not that I know anything that helps other than trying again, but at least now you know thee's more people with this problem.