Thanks scook, it was already checked.
It turns out that things also work fine during playback. So with things moving, either record or playback (even with nothing to play back, no clips) the audio engine keeps going and my virtual keyboard works as expected.
The track's input echo button works as expected during playback and record.
But with things stopped, I see midi activity but the audio engine is stopped, so no sound.
Input echo turns the midi activity on and off.
I can turn the audio engine back on, and it'll work ok for PRV, but the minute I touch the virtual keyboard window the engine shuts down. The keyboard notes activity continues to be reflected in the PRV keyboard.