USB3 card reader/USB3 port/standard SD card = drive letter
USB3 stick/USB3 port = no drive letter, not listed at diskpart.exe, a removable disk
I suspect USB2/USB3 mode. xhcdrv.inf contains a xhci parameter line.
hivesys.inf
HKLM,"SYSTEM\CurrentControlSet\Services\Wdf01000","ImagePath",0x0,"System32\Drivers\wdf01000.sys" ;xhcdrv.inf: 0: by port (usb2/3 port: usb2/3 hub port status), 1: xhci - default 1 HKLM,"SYSTEM\CurrentControlSet\Services\xhcdrv\Parameters", "RootPortStatusFormat", 0x00010001, 0.
Now:
USB3 stick/USB3 port = drive letter
I suspect USB2 mode at first reboot now. PNP overwrites this settings later.