AFX renders do not match previews

I am having many, many problems trying to render a project that previews perfectly in AFX. I often find that I will build a project that appears to work in AFX, only to, hours and hours later, find out that AFX won't render it. This is, as you imagine, quite frustrating.



I'm having two problems, now:

1) multiple clips, from multiple sources/frame rates (30fps and 29.97) preview perfectly well (any drift, for the sake of this post, was post anticipated and within nominal limits). There are several composites of the same material, scaled and placed in the same frame.

Again, on preview, everything works as expected. Also, a short, 60 second full res render works as expected.

However, when rendering the full 45 minutes of the project (where there is no animation, no keyframes, just static panels scaled and position in the frame without moving) the renders are heavily artifacted.

The only difference is how much of the timeline I render. All other settings are the same.






2) if i perform test renders of around 120 frames, all of the clips, no matter where I render, maintain sync. If I render large pieces of the timeline, the clips drift out of sync.

Yes. Weird.
If you're in a rush ...

... you've probably considered this, but can you do the composite in an editing app?