Had the same issue on the 2015 red. It looked so crummy, I worked on it, slowly but surely, and got it all off. (Presume third brake light is the town of lights, down the center of the fin- that is where it was one mine.) Does not appear to have surfaced on the 2016, but I only have 4200 miles on it.
I just discovered the same thing a few minutes ago on my 2019. I'm not worried about it, with a little elbow grease, it rubs right off and leaves a clear shine behind.