It appears I've got a successful workaround for the random and frequent cut out of my left audio channel with Piano V2 in standalone setup. Yesterday on my KeyLab61 mkII I switched ANALOG LAB mode to DAW mode. (there are 3 mode options (ANALOG LAB; DAW; and USER). I had been using the ANALOG LAB setting all along before that. After the switch to DAW mode I went a whole couple of hours without a single left channel cutout.
Today, I've had the controller and Piano V2 open for almost 4 hours, playing with it on and off and again not a single instance of left channel cut out.
I'm assuming that ANALOG LAB and Piano V2 are discrete and separate applications. Could it be that in selecting ANALOG LAB mode I was inviting conflict or this sort of aspect of function not working?
Anyhoo, I've had a clean slate, incident free for a couple of days with this one simple switcheroo move. That's great, I'll take it!