Interesting post i have recently encountered this exact problem with Arches platine and can vary from print to print, i have since added 1 drop of tween to 2ml of platinum/palladium sensitiser when mixed,(Tween is a polysorbate surfactin and has the effect of decreasing the surface tension of the mixed sensitiser which allows more adequate wetting of the surface fibres of the paper), the problem has not been eliminated but is significantly improved, and i have smoother results, it does seem as though there is a slightly colder hue shift with the tween but i would expect this could be counteracted with me heating my developer. Adding two much tween will result in water spots which will appear in the final dried down print.

Before the tween i would have around 6-8 passes with the rod, now its only 3 with a drop of tween before the mixed sensitiser runs out. My darkroom temp and humidity is 15C and 50 rh respectively and i use Potassium Oxalate as developer so i dont use Ferric oxalate solution 2, i found that that mottled a lot of my highlights.

I was reading Stan Klimek's comments in the Dick Arentz book on platinum printing last night and i found his comments quite relevant to what platinum printers go through :

'The quest for the perfect platinum print is similar to aiming at a moving target. After all these years, I still learn something new every time i print. Techniques I’ve been using become ineffective. Materials change or another printer comes up with an improved procedure. But after i chase it down, work it through, and come through with an image i am satisfied, I am allowed to relive the moment that i made my first platinum print.'

I am having similar problems with Kalitypes and will give the tween a try, if not I will have to ask the master of the process ‘Sandy King’ for some help!