I did get the problem solved with the help of Ring telephone tech support.
Here are my notes:
Possible source of problem: Perhaps the Ring repeater/extender was just far enough away and yet close enough to the Schlage lock that it was communicating incompletely: partially but not fully. I have since moved the Ring repeater extender to an outlet closer to the Schlage lock.
Solution: Ring telephone support did a command from their end to remove and forget the device entirely and as part of that process, rebooted my Ring Home Base. We did so with the battery on the Schlage lock disconnected. It is not clear whether or not we could or should have done the same thing leaving the battery connected. However, without the battery connected, the Ring system obviously could not communicate with the Schlage lock and apparently left the lock thinking that it was still connected to the Ring controller. Accordingly, when we reinstalled, it still gave an error message. We uninstalled successfully that time and then reinstalled successfully with everything working fine. An important part of the installation process at that time, however, required that we place the Ring base controller right next to the slide lock to make sure there was excellent wireless communication. To do that, I had to disconnect the ethernet connection and connect to Wi-Fi instead.