I have exactly the same issue! If I run the NKI diretly from my downloads folder on my macbook, the skin is fine. If I run it directly from the folder I want to keep it in on an SSD, or from Kontakt, or from Kontakt inside Logic I get the same issue as you. Some clash with a library called Autumn Strings?
I thought someone at Pianobook admin had mixed up their downloadable files, but no-one else seems to be mentioning this issue.