Sniffer are hollow ground and the blades are not straight when they come out of the package.
I start fy flattening each side on a belt sander carefully wil maybe 220grit or 320 grit. Then once they're flat I go to sharpening stones, progressively finer.
If you don't flatten them and you try to sharpen them on a flat stone, only the tip and the back end of the blades contact the stone. The middle of each blade is above the stone surface and isn't getting sharpened.