I’m sure you’ve had this, multiple render layers, different shaders on each. Eventually, it will break. Especially if you’re assigning materials on a per-face basis.
It’s better to not do that. But, whenever you have a scene that breaks and your renders are unpredictable, you can use this to fix it.
fixRenderLayerOutAdjustmentErrors;
Run that MEL command. That should fix some of the errors. Sometimes, it will revert whenever you save and close the file, but you can run it again … Read the rest