I have no association with RB but I thought it important to provide technical information regarding Bro's comments above. Based on his conclusion that the rotors were the issue - which would be extremely unusual in my extensive track experience, I went to the RB website to review the "comments in the forums".
I was not surprised to find exactly what I suspected - some folks did not understand that pad transfer is the result of the pads being operated outside the proper temp range for the pad and thus the pad smears and adheres to the rotor. Additional brake cooling and or changing to a proper heat range pad can prevent the over-heating of the pad material and transfer to the rotor.
This has also been the case with OEM BMW and aftermarket rotors when the incorrect pads for the conditions are used. In Pro racing many teams change pad compounds, rotors and brake duct cooling for each track and ambient temps.