I have had problems with this paper for several years now, even in a 10% Oxalic bath. I've recently found that Sulfamic acid is really the bees knees and works wonders with a couple of my favorite papers. I'm seeing 1.4+ dmax on some papers. I am looking forward to trying Rives in Sulfamic as I'm guessing this will solve the problems. You can find more info on the altprocess list.
You can find it at Home Depo if you want to do a quick try.
Mixes up a gallon.