More information is needed. What brand/model of TV. How is the TV accessing the My Cloud; DLNA or some other method? What is the Twonky administration page (http://wdmycloud:9000) indicating for Media Receiver type (Settings > Sharing > Media Receiver), does it match your TV manufacturer/model? If not what happens if you change it to match your TV manufacturer/model? Is Media Serving disabled/set to Off (via the Dashboard > Shares) on the Smartware and Time Machine Shares or other Share(s) used for backup or file syncing (like with the WD Sync program)?
Have you read through the following thread?
https://community.wd.com/t/faq-twonky-dlna-media-server-setup-use/95373
