Just to close this off, the problem went away after one of the OS point upgrades. I had built a workflow that carefully went around this, so I'm not sure when it happened.

FWIW I finally got an answer on Stackoverflow with some promise. orj says: You could populate a test database on a device then dump the application data container (see https://www.codementor.io/@paulzabelin/xcode-app-data-suni6p4ma for a tutorial) and use that container in your UI tests. This looks like a pretty good idea.

Thanks a lot for the replies and thoughts. Do people have favorite resources for learning the ropes as a small business? I've been reading "Small Time Operator."