@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.