I just bought a Pencil for my iPad Pro. When I drag the pencil across the surface, the resistance I'm feeling isn't consistent. It's almost as if the tip is occasionally hitting something on the surface that feels a bit rough or sticky. It's perfectly smooth for a bit of a stroke, then it gets all sticky/draggy. I'm worried that the Pencil tip might be defective and not uniformly made? Is this normal? I don't see any scratching happening on it- and it's a brand new pencil that's never been dirtied or dropped.