Without seeing your precomp it could be a blend/transfer issue. Some of the blend functions don’t work right when there is no background layer and the continuously rasterize can make it worse.
If the precomposed layer is 3D or the precomp layer is 3D in the outer comp the CR button can have an affect on that was well.
As for the shadow there are number of scripts on aescripts.com that let you do reflections or shadows or you could use videocopilots free VC reflect plug in, or simply flip a duplicate of the precomp or use the transform effect. That way you only have to animate the seal and the “shadow” will follow along.