Hi Jag,
I did some research and found an instance of one Unity administrator restarting the Unity server via the systray icon to resolve his issue with subscribers hearing failsafe when listening to broadcast messages.
Before you initiate a restart, though, you could probably gain some insight into the problem by checking errors/warnings that correspond with the subscribers' hearing failsafe in the Event Viewer Application log. If that doesn't get you very far, I'd suggest opening a TAC case.
I hope this helps.