Can you FTP to the My Cloud from a local computer on the same local network as the My Cloud?
Have you checked the port forwarding (if enabled) FTP port to ensure its IP address is the same as the My Cloud’s IP address?
If one isn’t using a reserved or static IP address on the My Cloud when the My Cloud reboots it could obtain a new and different IP address. This will break any fixed port forwarding rules configured on the network router/gateway.
Also, if you haven’t already done so, double check the My Cloud Dashboard > Settings > Network > FTP setting to ensure its set to ON.
FTP to a local My Cloud is working fine on my local network post firmware update.