I found the Field Dominance setting. Thanks.
I did some further brief testing and found I can get stabilization to work if I re-import my clips but disable all of the automated analysis and transcoding functions during import. (The clips were originally imported in iMovie from AVCHD files on memory card - now ProRes 1080 60i. I imported clips from the iMovie event directory into FCPX).
I drop the clips into the timeline, trim, add transitions, etc, then select all of the clips I want to stabilize in the timeline and select Stabilization in the Inspector. FCPX then analyzes and renders in the background. I did not change the Field Dominance setting prior to selecting Stabilization.
This is alot like the old way in FCP7, but its the only way that works for me at the moment. Takes a long time too.
So for now, the issue for my workflow is:
Transcode your media and analyze your media during import = Stabilization will not work, at least with previously imported ProRes files from iMovie.
I've experienced similar occasional stabilization failures in iMovie and FCP 7. I have not identified a common thread yet.
Maybe yakudza77 has found insight. See above.
Thanks for your help.
I hope this gets sorted soon.