First, to respond to notfred's suggestion:
The voltage measured at the 12V aux battery before starting the car was 11.99V.
The voltage measured at the 12V aux battery after starting the car was 14.40V.
That tells me that the car started OK, and the normal charger for the aux battery is working.
But, notfred's question about the aux battery made me think. We had one or two prior situations in which things got really screwy and charge scheduling didn't work. After fooling around with the aux battery in those cases, I realized that one of the things I had done was to disconnect the negative terminal of the aux battery. Then, later reconnected it. That fixed the previous problems. It also reset a bunch of stuff on the dashboard. I figured it probably forced reboot of the computer.
So, after taking the measurements, I disconnected the negative terminal of the aux battery. Waited about 1 minute. Reconnected the negative battery terminal.
VOILA! PROBLEM SOLVED! EVERYTHING BACK TO NORMAL.
My bad. I immediately suspected hardware (because of the way the problem first manifested).
For totally unknown reasons, it was software, and a reboot fixed it.
Guess those Microsoft technicians know something after all!