That is not necessarily the case. While it may be limited to those devices using the USB 3.0 protocol, For some users they don’t have problems with attaching a USB 3.0 device to their My Cloud. In my case I have two USB 3.0 devices, one (a Toshiba Canvio external hard drive) wouldn’t properly mount or be seen by the v4.x version My Cloud until I deleted all the partitions, created a new single partition then formatted it. Since then no problems with that USB 3.0 drive and the My Cloud. On the second USB 3.0 device (a cheap no name docking station from Amazon) it was hit or miss with certain SATA hard drives on being mounted properly by the My Cloud. For what ever reason a Seagate 1TB hard drive in that docking station wouldn’t mount properly from time to time with the My Cloud, yet a 500MB and 250MB SATA hard drive would mount without issue every single time.
That is part of the problem here, its not consistent problem every single person experiences or people with certain specific USB external hard drive models seem to experience. Worse if people don’t open up a support case and submit their logs to WD support, WD cannot properly investigate or compile data to help determine what might be causing this strange issue that some of us have experienced.