I find this happens in 2 cases.
Case 1: improperly logged in. To check this, go to chat #zk and see if anyone is online or if chat does not load history. Solution: log out and log in. No restart required. Frequency I get this: 15% of the time(of all startups).
Case 2: battle list stuck on old battles and does not update. After keeping chobby open for a long enough period and playing(I don't know what triggers it) battle list does not update. You cannot join new rooms, the state of the rooms(in battle? Players in the room?) Is incorrect, and trying to spectate matchmaker games that have finished results in nothing. Requires restart I think? Happens sometimes.
Edit: windows 10