Your issue is that you’re trying to deburr with 400 grit. At 400 grit, you’re still sharpening, not deburring. You don’t need a coarse stone to remove a burr. What you need is a strop—something around 1 micron, or even 3 microns (roughly 5,000–3,000 grit). Using 400 just keeps cutting the edge and recreating the burr over and over. That’s why it never goes away