Looks like they might have cleaned it with something that has caused the top layer of plastic to fade/degrade.
only time I've seen something similar was on a old film camera of mine and the back went all hazed like this because of a cleaner I used, same deal if I scratch it with my nail it comes off.
As for suggestions on removal I just kept using nail on the camera but it was a much smaller surface than you have here and that would take an age.
Good luck with it though hopefully someone else has an idea.
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