I have a Comp of a cartoon character that is being nested into another Comp.
The nested cartoon character Comp is supposed to fade into the final Comp...
...but as it is fading in, it looks like all of the layers are fading in invidually. I am not explaining this very well. See the pics below.
Nested Comp At 50% Opacity
Nested Comp At 100% Opacity (which is the way it's supposed to look)
The only solution I've found is to pre-render the first Comp, and insert that movie file into the final animation. But I would prefer not to do that for various reasons. Is there an easier fix?
You are using collapse transformations/ continuously rasterize and thus the behavior is normal. It is an oft-ignored and oft-forgotten fact that not only it retains 3D magic on 3D layers and keeps vctor artwork sharp, but it also passes through blending operations from pre-comps. Turn off CR/ CT if you don't want the behavior or apply an effect that enforces rasterization and then use e.g. the Blend effect for the fade-in.
Check your blend modes. Set all to normal and the problem should go away.