Regarding USB 3.1 issues:
I used to carry mid range small sticks and experienced major problems with NXS2 units. These sticks worked perfectly in any other player but for some reason the latest genration players seems a bit picky. I blame cheap controller circuits.
After this post I got a pair of Samsung Fit Plus and experienced no problems whatsoever. But since the price point for Sandisk Extreme Pro sticks have dropped recently I highly recommend investing, they are lightning fast!