Thanks for the tip. I have now stabilized my footage in Motion 5, but have come up against an incredible bug on export. Even though I set Borders to ‘Zoom’ it exports the footage as if Borders were set to ‘Normal’. The footage plays back as expected in Motion 5, the RAM preview is as expected, even the little preview window before export looks ok. But the ProRes export from Motion does not match any of that. Same result whether I export directly or via Compressor.
This is a lot of work that I now can’t do anything with. Very frustrating.