Passivation in Coating Pan (Pharmaceutical)

We have done passivation on coating pans, that we use for tablet coating (pharmaceutical). The passivation was done by third party before 2 months. but somehow, when we coat white tablets with white water based solution, it gives scuffing marks on tablets, kind of black specks. we are suspecting this is happening because of passivation (poor). Is there anyway to check that they have done good/bad passivation job. Or what might be other reason for scuffing marks on the tablets?