I'm working on a typographic animation where I use a lot of objects with holdout shader to mask out different parts of the scene when they shouldn't be visible.
When I render the animation, some parts of it produce black frames, or contain black rectangular shapes that I didn't intend to appear. The blackouts are consistent between the renders.
I tried moving verticies of the holdout objects, flipping normals - chaning the BVH setting of the scene - that didn't help. Sometimes rotating the holdout objects slightly makes the blackouts go away, sometimes adding a Solidify modifier helps, but I wasn't able to get rid of all of the artifacts.
For example frame 224 of the animation renders like this:
But in the viewport Cycles preview it looks as expected:
There is a plane with a holdout material present there, that's used to hide one part of the "MUSIC" text. The black shape in the final render is somehow dependant on that plane - this might be a good trace to find out what causes th, ese artifacts.
Here's the blend file:
Here's some renders of the animation to inspect the problem:
You can see how the last part of the videos are completely messed up - the cartoonish explosion scene is completely messed up with the blackout frames.