+ AA6YQ comments below
He suggested a sequence of not starting the router automatically (which wasn't the case anyway), upgrading, then starting the router. He also pointed me to a version of the software that actually had been released that day (last week). Unfortunately, no joy.
+ What was Joe's response to your "No joy" report?
+ Microsoft is clearly making it tough on device manufacturers like microHam with Windows 10 updates that seem egregiously destructive, so I'd be patient. But I also wouldn't give up after the first recommended action doesn't solve the problem.