strange: USB 2.0 - yes, USB 3.0 - no

[heinz57g]

very strange, at least for me, after using hundreds of USB sticks over the years:

got 2 CORSAIR Flash Voyager Slider X1 (64) for Xmas, clearly sold and marked as USB 3.0.

they both work on every USB 2.0 port i tried - slow - but without fault. but on several USB 3.0 ports (three laptops tried, two desktops, 4x WIN7prof, 1x WIN10prof/latest) they simply do not show up.

one i am using, though on USB 2.0 only - shows no fault even after many writes/reads.

the other one i am experementing with, reformating in all possible ways, but i get nowhere - still not recognized on any USB 3.0 port.

any idea, any suggestion? i am travelling at the moment, but have access to enough computer equipment to try whatever might be needed.

greetings - heinz -