SONAR X3 I see the note in piano roll but I don't hear it

Problem: I suddenly stopped hearing a note in the midi clip, though I can see it in the piano roll:

In the image, the silent note, that I can't hear is selected.
I've circled the selected (darker) note, as well as a full overlap, to show it's not the closeness of the other note that's causing it to be silent.

Solution: Stop playback and start again - problem went away!

good luck!

d