Ànother user reported the same problem with the at&t Uverse router recently. It appears that it fails to auto-negotiate a link speed, and fails to establish any connection.
I suggested a workaround of putting an Ethernet switch or old router between MyCloud and router, and this user and others found this to allow a connection to be established.
It’s unclear whether the problem lies with MyCloud or at&t, but the MyCloud obviously works with plenty of other routers.
A forum search should find the thread.
