The solution is to render only the topmost track containing Sapphire effects. If you render any lower track first, or all tracks together, you may get incorrect results depending on the order Avid happens to process them. When you render only the topmost track, it should automatically render the lower tracks correctly as needed.  If you already have bad results, first delete the incorrect prerender clips for all the affected tracks (top and all lower ones) or just change a parameter in an effect in the lowest track, which should cause the other tracks to become unrendered.