Just a quick guess here, but Arches Platine is extremely sensitive to changes in the weather. During the winter it will often have a hard time absorbing the coating solution into the fibers of the paper, and it ends up giving poor results. You can try soaking the paper in a tray of 1-2% oxalic acid solution (or citric acid if you don't have oxalic) for a few minutes, before doing the emulsion coat. After soaking you should let the paper dry completely, then put down your normal mix of pt/pd.
You should get a better Dmax and hopefully get rid of the bronzing effect. Another thing I've also noticed is that Arhces Platine and Bergger COT-320 both need some sort of contrast booster added to the mix to cut down on a base fog that they often show. A drop of Na2 Platinum or a few drops of 3% Hyrdrogen Peroxide added to your bottle of Ferric Oxalate will clean up your higlhights and give you clean borders, if you're masking them.
Good luck!