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I have not heard of this problem, but yes, vinyl materials weather with time, esp. if exposed to finger oils and skin acids.
My own idea is, that you might want to put a trifle (a very small amount) of some relatively odorless oil (whose aroma you don't mind) on a clean cloth, and wipe those areas on the keys with it, now and then. That might 'fill in' the roughness, and also clean anything from your fingers that might cause further erosion of the surface.
On the other hand: if you use any sort of organic oil in this fashion, it may become rancid with time. Not a favor to do your keys to say the least.
And I advise strongly against using Windex or ammonia cleaners! they will erode your keys further, or otherwise alter them in ways that are not good.
A search for similar complaints or concerns about Roland Fantom keys turns up this:
which is about Fantom keys being too slippery - and mentions sandpapering them - and I'm not sure what to think. But if you use sandpaper, try it first on the least critical surface of the keys, a location you would not mind ruining, and see how damaging it can be, before applying it or trying it.