I know it is ancient but it is what I am using. My WDCloud 3TB drive has an 8TB drive connected to it via a usb connection. I watch videos on my TV through my network and most of the time it works good. On occasion, it will fail and it may take a while to come back or not come back at all and I will have to reset it. I know there could be a million things wrong with what I am doing.
Note that the v4.x firmware My Cloud is OS3 not OS5.
How is the TV accessing the My Cloud? Using DLNA (My Cloud Twonky Media Server) or by SMB?
Have you checked to ensure you are not having a network or WiFI problem between the TV and the My Cloud?
There is a Twonky FAQ that has additional information and suggestions that may help if one is using the My Cloud Twonky Media Server.
Have you checked the User Manual, Chapter 12?
How often do you reboot your device? I reboot mine every week.
My old OS3 WDMYCLOUD is connected to my home network, wired to my router. My router is a Linksys, MU, MIMO.
