I have an FCPX library with a bunch of assets and a number or projects. The projects consist of muti-camera shots of a conference with a powerpoint on stage. I have replaced the filmed power point with a scaled computer quality original on a lane above scaled to cover the original presentation. All is good until speakers change and someone walks past the slide of course!! I have addressed this with an animated mask on the inserted image, all is good and works as expected on my laptop.
I have then exported the event XML from my laptop and imported into the desktop project. When I play the project, the speakers end up behind the image file. When I stop play and click on the computer image version, and skim, I can see the mask points all animating. So it is there, but it's not applying any alpha characteristics to the clip below. The laptop one works, the desktop one doesn't.
I have done a number of tests now and it does, as you suggest, seem to be linked to the XML export which appears not to export everything, rendering it only partially useful. I thought the whole point of the new fcpx xml format over the older FCS format was to include additional meta-data / fields & structure to be able to describe everything about the media and timelines, so maybe this is a bug, after all, the project, or timeline, is just a bunch of meta-data!