I would suspect it's the Metaball Object. Corona works with so much of C4D, but funny things with Mograph Instances, the Background Object and I suspect Metaballs too. You didn't mention if the red sphere was also a Metaball. Is saving to Alembic a form of baking all the animation into the scene? If so, you should be able to scrub the timeline without weird things happening. Is the animation playing out as expected, with the Metaball effects, just without blur?