As stated above, I tried to commend a player (out of excitement!) before the scoreboard appears at the end of the game and it just froze for a while.

Afterwards the scoreboard appears, but the only thing I could click was the button to send me back to the dashboard. Also, it appears that the 'You got an item' doesn't appear too (except for a red box outline to tell you that you were given an item)

Next Steam will put you on offline mode, stating that there's no network connection available.

(which may, or may not be the cause of this, however it would be too much of a coincidence since we were relatively lag-free throughout the whole game)

Hope this helps!