I had the same problem when I first started using Platine in the mid '90s. None of the single ingredient clearing baths would work, no matter how strong or how long.
Kodak HCA (or similar hypo clearing products) used at regular working strength (as for film or paper) in the usual method of 3 successive clearing baths should do the trick.
To make your own clearing bath from scratch I suggest the following:
2 Liters waterAdd the ingredients in the order given and be sure each has fully dissolved before adding the next. The citric acid converts the EDTA to the more reactive disodium form. The sulfite seems to be the critical ingredient in getting Platine to clear properly.
2 Tbsp EDTA (tetrasodium)
1 Tbsp citric acid
1 Tbsp sodium sulfite
Also try eliminating the water rinse between the developer and first clearing bath. In my experience, it actually has an adverse effect on clearing.
Hope this helps,