Re lap your SG20, some do not stay flat and smooth, bevel or round the edges, make sure all the previous stria is removed prior to going to the 20K. there should be no deep stria on the bevel.

Make sure your Chrome Oxide is razor quality, only a few are, quality Chrome Ox is not expensive. Try pasting a piece of cardboard and leave the balsa out of the mix.

Look at your edges, the vast majority of edge issues stem from bevel setting or lack thereof. The edge is only as good as the prep.

Improper stropping on a weak edge just compounds the problem. The problem with razor honing is to build a good strong edge, every step matters.