Thanks, SparkE. One difference between my experience and the one described in that thread is that his car was left unplugged for a month in cold weather, and mine was left for less than 24 hours in a garage. He didn't give much detail about it, but it seems that jump starting, which one would expect to work because the Owner's manual gives directions for it, did not work for him, either. The service manager couldn't explain why it didn't work for me and said he would consult a GM engineer and get back to me---a week ago. Chevrolet Customer Satisfaction said someone would call me back within two business days---five business days ago. Oh, well.
SeanNelson, I understand what you are saying about what should happen. However, I am uncertain about how confident I can be that what should happen will happen. What should happen is that a Bolt EV that had just been driven 10 miles at the end of which there were no in indications of problems, and that had 150 miles of range left when was it was turned off, should start without problems 20 hours later, but mine didn't. What should happen is that a Bolt EV with a dead 12V battery should work after being jump-started, but mine didn't. What should happen after a year-and-a-half-old car malfunctions so badly that it has to be towed to the dealer is that the problem is identified and corrected, but mine wasn't.
As it stands, even if I'm not at risk of loss of control at speed, I am at risk of having an inoperative car whenever I park it and leave it unplugged, which means that I risk significant inconvenience if I use the car in a way that even approximates normal use.