Ditch the Ferric oxalate solution number 2 except in tiny quantities. It is awful stuff and can cause grainy prints. Most printers now use Na2 when they need contrast control. The white dots sound like the paper has some buffer in it still. Which would be weird with Platine. I'm not sure about that. You could try acidifying the paper with 2% oxalic acid prior to coating. The other thing is that you might want to consider using potassium oxalate as a developer instead of the ammonium citrate. It is generally smoother and warmer toned than AmCit. Finally, the glass rod may be an issue. You really ought to get a 2 inch Richeson 'magic' brush. Your prints will show an immediate improvement.