@lakotaubp Update: I followed the guide at https://forum.xda-developers.com/t/guide-return-your-opo-to-100-stock-current-build-cm13-1-2-znh2kas3p0.2826541/ to return the device to a sane state. Then started from the beginning with ubports. Much smoother experience this time -- didn't even have to manually select Oneplus one, it was automatically detected. So now I'm up and running!
Thanks.

@lakotaubp Update: I followed the guide at https://forum.xda-developers.com/t/guide-return-your-opo-to-100-stock-current-build-cm13-1-2-znh2kas3p0.2826541/ to return the device to a sane state. Then started from the beginning with ubports. Much smoother experience this time -- didn't even have to manually select Oneplus one, it was automatically detected. So now I'm up and running!
Thanks.

@lakotaubp Thanks for the suggestions. I went through them a few times, but the end result has been the same each time. Anything else I can try?

Installer reports success, but phone just repeatedly buzzes and flashes the Oneplus logo, the text "powered by ubuntu" and "supported by:" followed by a ubports logo.
I can get to the UBports Recovery menu pressing Volume Down and Power at the same time, but don't know what I can do from there that will be helpful.
(I've used different versions of the Installer without better results.)
Any help would be appreciated.
Thanks.