Boy its been a few months since anything's been written in here......and I hate to break the record but I think there's something odd with the effects/synth window.
If you playback with an effect on an audio track and you turn it off with the green light (power) in the top left hand corner of the effects window and turn it on again, the audio sometimes isn't there.
The solution is either remove the effect and your track comes back or stop and start the playback.
Seems to happen to a few of the pluggo effects and a couple of others.
Could have something to do with the way the plugin has been written?
Then again the red bypass button/light doesn't cause the same problem.
It's not a biggy.....I just need to remember to go for the bypass instead of the power.
(yes I'm still in Jaguar if it means anything).