There's nothing in the Messages saying why it has stopped?
I'm a traitor to myself and my people by doing the Windows thing, but it gives messages when it starts and stops processing and so on. eg: 'processing stopped; user is active', if you've set your prefs to 'stop working when the computer is in use'.
There could well be a log for the equivalent messages in the Linux version.
PS: Mysterious team member #5 now exists on the group list...
Two out of three people wonder where the other one is.