Is the riving knife attached to the bracket with a slot or a hole? A riving knife mounted with a slotted hole can be extremely dangerous. If it comes loose, it can launch directly at the operator. Thought those were illegal. What are you using for a blade? Looks like a negative hook miter saw blade, pretty poor candidate for ripping. Almost looks like the mounting bracket is not in line with the blade, shimming won't change that. The riving knife must be the same thickness as the blade and perfectly in line. They make different riving knives for thin kerf and regular blades, they are not interchangeable.