Flame Planar Tracking Occlusions - aspect snafu?

Hi All,

I’m on Flame 2020.3.1.
I’m seeing weird behaviour when planar tracking using occlusion. When I use the GMaskTracer the occluding gmask seems to be offset relative to the main target shape. This doesn’t happen in action as far as I can tell - see screenshots.
Footage is 3k but 16:9 ratio, which I thought might be the issue.