How to debug USB storage issues on a MacBook? I'm trying to diagnose the USB key of a friend of mine, who says it works in his Windows but not in his Android tablet (Samsung).

When I plug a USB key in my MacBook nothing happens. The device does not appear neither in Finder nor in DiskUtil, for example diskutil list does not show it.

I looked if something is logged in /var/log/* when I insert or remove it, the only thing I see is this message in /var/log/kernel.log:

May  4 19:38:38 mymacbook kernel[0]: USBMSC Identifier (non-unique): 0x1307 0x163 0x100


I'm plugging the USB key directly in a USB port on my MacBook. I tried both of USB ports, same result. I don't know how the USB key was formatted.

Any ideas how to proceed in diagnosing this?
In the past using Macosx El Capitan, I would sometimes see
the message USBMSC Identifier (non-unique) in dmesg
after I had disconnected my external drive and tried to 
reconnect it later unsuccessfully.

My blackbox perspective of what was happening is that upon
the attempt to reconnect, the already cached mac id of the
usb device was recognized as already existing, but interpreted
as a different device, so the "reconnect" failed.
In that case, I disconnected the external drive from USB again,
powered down both the drive and the computer, waited a short while,
then reconnected the drive and booted.  The id was found as 
unique again and the mount of the external drive succeeded.

I see the same log message upon another error in 
Sierra 0.12.6, however. I'm seeing the USBMSC Identifier (non-unique
log message when I'm not able to mount an external drive which 
has the same vendor ID as another previously connected external
drive, but different complete mac ids.
I haven't been successful at getting the OS to recognize the
second drive as unique yet.
I haven't tried to mount the drive using another OS yet, but thought
the "reset" scenario above might be helpful.