I bought a multiport adapter and had a problem with My Book Duo USB. Reading was fine at 120+ MB/s but writing would top out at 30 MB/s and the connection would drop out constantly, not being able to complete a Time Machine backup. The solution was to get a Belkin USB-C to USB Micro B cable and connect directly to one of the port on the MacBook Pro. Seems the Multiport adapter does not play nice with external USB hard drives. So if you are having problem with an external drive, pick up a direct cable from USB-C to whatever port your drive uses (USB-A, USB-B, USB Micro etc).