Thanks for your encourangement.
The problem persisted over the weekend. It seemed to occur after the MBP awakened on cool mornings after it (and I) had been sleeping overnight. I took a 10 second video of its recurrence (on and off and on and off) on my iPhone, and yesterday took both to the local Apple store. They accepted that it was repeatedly occurring and merited replacement of the MBP with a new one at no cost to me. However, I had to either reorder another online (charged to my credit card), and bring the 'old' new one to exchange with the 'new' new arrives in two weeks, and then receive the credit on my card, or leave the machine with them and they would call when the new one is available. Since the 'old' new one is still viable, I elected the first option.
I can only hope that there is no repeat problem on the 'new' new one, which would imply a software problem. I doubt it will. This is the first 'lemon' that I have had since I started buying Macs in 1984.