My Cloud OS 3 Remote Access used the following ports and allowed the user to manually configure port forward on the device itself.
Internal HTTP 80
Internal HTTPS 443
External HTTP 9000 - 9999
External HTTPS 9000 - 9999
My Cloud OS 5 only uses HTTPS and does not allow the user to manually configure port forward on the device itself.
OS 5 depends on UPnP to manage the forwarding of the ports.
Internal HTTPS 4430
External HTTPS 40000 - 49999
fritzbox-7490 Setting up automatic port sharing
https://en.avm.de/service/fritzbox/fritzbox-7490/knowledge-base/publication/show/894_Setting-up-automatic-port-sharing
Based on the information listed above I would suggest:
- Toggle off and on Automatic Port Sharing / UPnP
- Check the firewall is not blocking all ports between 40000 - 49999
- Reboot the router
- Reboot the My Cloud