Thanks for posting and sorry for the late response.
A few questions — is this only happening when casting the video to your TV? How about when watching it directly to the YouTube app? What troubleshooting steps have you done so far? In the meantime, you may try to reboot your Chromecast Ultra and uninstall and reinstall the YouTube app. Rebooting your phone or using a different mobile phone might also help.
Keep me posted.
I think this is sorted. It seems that even though I'm selecting to cast through the Chromecast ultra, this directs it through the YouTube app built into my TV. Once I signed into the app on the TV it all worked.
Thanks for replying.
Thanks for keeping me in the loop and glad to hear that this has been sorted out.
Since the issue is now resolved, I'll lock this thread. Should you need help in the future, feel free to start a new thread and we'll be more than happy to help.