I thought I would post this again as I have isolated the issue
Repro:
1] New project
2] New instrument track, instrument loaded - loop a few bars ensure you have sound.
3] Mute the track (whilts it still looping) result silence - the correct result
4] Disable the muted track
5] Re-enable the muted track - Here you will notice that the mute button is not active (yellow) , but the project is silent as if the mute button is armed. Because the track has been re-enabled and there is no active mute shown, you would expect the track to sound. Or, the mute button to show Yellow.
There can be days between disabling and disabling a track and if you do this frequently it is impossible to keep tabs on what track was muted when disabled. Considerable time can be wasted hunting down the cause of the silence.
You can search high and low for sound in the usual suspects and find nothing - until you randomly hit that mute button (seemingly to MUTE it) when it is silent.
A couple of clicks on the mute and solo button and your track will work again.
Definite bug.
Z