I had the same issue on one of the diamond cut alloys on my Mk7.5 GTI and I raised it as a warranty claim with my local VW dealer. Their After Sales Manager, initially, tried to argue that it was down to stone damage but I wasn't letting him off that easily.
I stood my ground and pointed out that there was absolutely no evidence of any break in the lacquer, and that it was deteriorating under the surface, so was obviously a manufacturing defect. I had to book the car into their body shop, where they examined the wheel thoroughly (under a microscope, I think!) to check whether it had been repaired but they eventually conceded the case and ordered me a new wheel. It arrived and was fitted the following week.