Can't update from v62.1

Running v62.1 on a pi3. The dashboard says:

Home Assistant 0.64.3 is available
You are currently running version 0.62.1

When I tell it to update, it spins for a while, I lose connection to the backend (“Reconnecting”), and it goes out to lunch. I use putty to login and at the command line I “reboot” … the ssh window is disconnected and it never reboots. I have to unplug the pi and get it to boot that way. It comes back up on v62.1, having never finish updated.

It was doing the same when v63.* was available.

Short of re-imaging the sd card, how can I tell what;s wrong and better yet, how can I fix it?