OK, the problem turned out to be me, naturally. The solution was to use a hotspot instead of my hotel's wifi. Previously, I'd neglected the step of connecting the Bolt to the hotspot by turning to the wifi settings on the companion app. I had a vague notion that if my iPhone was connected to the hotspot, the app on my phone would be as well. Not so! Also, you can start the update process on the companion app, but must select install when it shows up on the Bolt itself. Now, my Bolt is happily reinstalling its maps.