Some sort of box which covers the screen depending on the position of camera and how far you are zoomed out. When you have picked your hero, your screen will be a lot further out than the default start, and when you scroll this box appears. (Several pictures) Notice the zoom unit is off the usual count. Most the pictures are +3000 zoom, and you can usual almost see the complete map at 3000. Happened twice so far. If I have to think in connection between the two games, both games were my first games as I opened the dota client, and both times I was host. So I have not been able to try reconnect ingame.