I have run into a problem with my RPi3 and uMate 15.10.3 not recognizing some USB3 devices including 2 different USB memory sticks and a Samsung EVO 850 running through a Sabrent SSD to USB3 adapter (JMicron 152d:1561). Oddly, it works fine with an older OCZ Onyx SSD connected through an identical Sabrent adapter as an external root. The Sabrent/Samsung pair and the USB sticks work fine on an x86-64/Mint 17.02 with USB3 ports on the motherboard but the RPi3 reports> Could not display “/media/paul/xxxx-xxxx”. The location is not a folder.< In the case of the RPi3/Samsung combination, the computer locked up and required a reboot.
I have tried this on an RPi2 running raspbian and it was able to display all of the above USB3 media without difficulty. Next is to try the raspbian sd in the RPi3…think it is the right version.
Loaded Raspbian from Noobs 1.8 on the Rpi3 and brought up the desktop and the USB3 devices work normally. This is a ubuntu Mate 15.10.3 or kernel problem. I do not know if it extends to earlier or later versions.