Help! Trying to use the Inflate feature but it's doing weird things to my shape!

I am creating some branch-like shapes in illustrator and trying to use the 3D and Materials > Inflate... to give it a more interesting look. Other branch-like shapes that created and used this feature on turned out just fine but for some reason, when I try to use it on a few other ones, I get some weird things happening like this duplication. (See Before and After pictures) Can anyone tell me why this is happening?