This problem I have happens only in Studio One V4. I did not have it in V3 (which I use with exactly the same set-up, but on a different PC). When an audio track is selected as active, it does not play back in V4. When I select any other track, it plays back. So there is nothing wrong with the wave.
It is like its muting itself. I tried several options to get it to play when the track is active - e.g. Unmute event, etc.
I can't find any similar problem in the forum (posts report on other silent problems, such as MIDI and several other issues).
I use an external Steinberg USB Audio interface - which works fine with SO 3. There must thus be some new setting in V4 that I need to do, but I don't know what.
I'll appreciate suggestions, as with this problem I cannot play around with audio changing settings while it is playing.