Losing output from tracks

Occasionally I lose the sound of one or more tracks, and find out that they have become disconnected from the (usually master) bus. Reconnecting the outputs solves the problem.

Question: Is there a secret track output disconnecting keystroke that I may have accidentally hit?

I’m encountering the same thing with Ardour 5.12. I’m just tweaking plugin settings when this happens, so perhaps it’s a bug.