Since this patch (or perhaps even the one before that, memory is a bit foggy), whenever I try to join a server from the server browser that appears to have an open slot, it may have filled up by the time I try to connect.
It will tell me that I cannot join because the server is full, but when I dismiss the message, the screen gets stuck on Attempting to join Session with a spinning wheel. I have to force close the game to get out of it, as it will never end up connecting.