Yeah, I get this too on my '17 reg 1200 S. Fine for a short period immediately after servicing, then it's back pretty quickly. Think it's pretty standard and, as michel says, generally seems to be build-up of dust / garden variety gunk, but not really a significant prob.
I've had this 'issue' on every Mutli I've owned, including a 2010 MTS, a 2014 Pikes Peak and now the 1260S. Irritating yes, any impact on braking; No. Any intention of doing anything to stop it; No as it will almost surely want repeating again and again and again........drone! Some things never change
