Good question! The answer to this one is not obvious – you need to delete the top faces in the middle of the plate. What’s happening is that the base is an enclosed solid while the outer part of the plate is one edge thin and not a solid. This causes weirdness because the normals don’t know which way to point, which messes with the solidify modifier.
To solve this, delete those middle faces at the top so that the whole thing is a thin surface. Then extrude everything up to make everything a solid and delete the solidify modifier. That way you can move the center up and not have a dip in the plate where the bottom lip is.
Hope that helps!
