Well, it just happened to me...
I noticed some people in my server so I might as well wreak havoc on them...

But there was the usual "Not Available" in the information box. So I played a bit of campaign, the first level and went back to play on multiplayer. Oh lookie! There were numbers! I could now join games and I would press Alt-F4 after a few minutes.

There's definitely something wrong at your end.