What grit sandpaper do you use to sand the contacts? Also, do you use the 510 adapter all day with zero issues? If so, it might be a broken adapter...let me know Imeo!
I use my adapter for 1 week with exellent results. It works so good that I am ready to forget the 901 atomizers Zai.
Better use eraser first. If you see that you need to sand them then use a 1500 sand paper to be sure that contacts will remain smooth