Port forwarding is done within the network router/gateway not on the My Cloud. When configuring the My Cloud Remote Access option to Manual one can change the default ports to alternate ports then use port forwarding within the network router/gateway to route to the alternate ports.
Check the network router and ensure UPnP is enabled when the Remote Access on the My Cloud is set to Auto.
Others apparently have had trouble with remote access when running two or more My Clouds on the local network. Here is a previous thread that may have some ideas.
https://community.wd.com/t/port-forwarding-for-two-my-clouds/137823
