Motion Generator appears fine in timeline/canvas, corrupted on export (missing layers)?

Question

I have a custom Motion Generator with a lot of layers & editable text fields that acts as an overlay to my video, so it runs through the whole project, broken up into clips whenever the text needs to change.
I recently finished my editing, scanned through the project in Final Cut (seeing no errors), and exported it. But when I look at the exported .mov, one of the generator clips didn't render properly. The text is there, but the background images aren't. This isn't even something I can toggle in my Generator, it just like... half-rendered.
The clips on either side were fine, and again, this only appears in the exported .mov. Within Final Cut Pro X, there is no way to tell something is wrong.
So I opened the project back up, found the generator clip in question, and tried disabling/reenabling it, then exporting just a tiny section to see if that fixed it. The test was rendered properly, so I went back and exported the entire project again.
This time, the original error was fixed, but in another section of the project (minutes earlier, in a different compound clip), the generator failed to render properly. This time, only half of the images loaded (rather than none), and a piece of text was rendered twice (once properly, once smaller in the middle of the screen, over someone's face).
And again... it still looks fine within FCPX itself.
Has anyone else experienced missing layers on a custom Motion Generator on export only?

Answer 1

Elated - I have found the problem and, more importantly, a solution.
While converting the original footage to ProRes, Compressor complained about one of the segments (the JVC camera records in around 18 minute chunks) I was trying to import. Sure enough there were some visual glitches on playback but FCP never seemed to care, but Compressor refused to convert it to ProRes.
Which got me thinking.... back to the timeline I went. Knowing which segment had caused Compressor problems, I isolated it, and cut out all footage with distortion on it. I had used b-roll footage to cover the glitches anyway, but this time I used the blade tool to remove the offending video on V1 even though it was being obscured by V2.
As if by magic, and to my great relief, the footage rendered and as we speak DVD Studio Pro has just spat out my first burn of the DVD (mind you it did take close to 6 hours to encode the footage to MPEG2!)
So there you go folks, corrupt video footage, even though it isn't playing was enough to halt my export and suck two days from my life. Lesson learned.