Just tried a stainless cup, and no static with a clean grinder. There was already less static grinding directly into an Aeropress, but none at all with the SS. (y)
Plastic/polymers absolutely can hold a static charge - otherwise "cling" film wouldn't work and you wouldn't have to ground PVC pipes in dust collection systems! The dosing cup might be polycarbonate or PET, Turin only lists it as "food-grade transparent plastic", but it definitely holds a...
I had the exact same problem with the exact same grinder, also in Hawaii... It didn't have the problem at first, then it appeared and got progressively worse, especially with coarser grinds. RH where the grinder sits is 50-80%, and I'm using primarily dark roasts and espresso grinds. I was...