No Audio but I can hear the metronome

Final update:

I had a gig yesterday. I am pretty comfortable that the two keyboards get swapped based on using different USB ports, either on my laptop and/or the USB hub (I could probably avoid this by being more careful and always using the same ports).

So, I noticed the keyboards were swapped.

No sweat. Went into the Rig Manager and swapped them back in about 30 seconds and went on to a successful gig. Worked perfectly.