When viewing the list of Shares on the My Cloud does it list your USB drive share twice? For example “drive” and “drive_1”? If so this is a well known and very frustrating issue with the latest WD Firmware. The solution is to remove the USB drive via the Dashboard by ejecting it, then remove the left over Share for that USB drive in the Share page on the Dashboard. Then reattach the USB drive, go back to the Share page and rename the USB Share back to the original name.
More on this duplicate USB naming issue is discussed in several other threads/posts, like the following:
https://community.wd.com/t/new-release-firmware-release-04-04-02-105-1-27-2016/148441/69
