Spigen Ultra Hybric Case - erosion and corrosion problem on back cover topic

I have realised that my back cover has some pitting marks(due to erosion or corrosion). I believe this is because of my case. I am using spigen ultra hybrid.
First I saw some white spots between case and back cover, then I removed the case and after cleaning the spots, I saw that cover has some marks.
Does anybody has this kind of problem with ultra hybrid?

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