Okay, so this has been a bug since the release of the game. If you put someone on ignore or block them via the friends list, it pops up a message for the steam overlay. If you don't click this message, when you open the steam overlay next, it won't be there and you'll have to restart Steam entirely to get it to go back to its normal functionality.
Could you please just remove the message that confirms it so this stops happening? Thanks.