Last night I uploaded an old project that was done originally in N3 and worked on again in N4.3 a while later. When I launched the project from the shortcut, it opened right up in N6 and told me that certain plugs from N3 were missing, no surprise there. What was surprising was that my lead vocal track and a couple of others were not playing. 
The rhythm tracks and BG vocals were all playing but there was NO SOUND OR EVEN LED INDICATION OF SIGNAL coming from the affected tracks. I soloed the track to check the routing and everything in the line opened right up. But as there was no signal coming from the source (which clearly showed nice healthy wavefile images in the project window), all of the output busses were blank.
Any idea of what’s going on here?