Hi there

Nothing has been reported as of yet through either this forum, or other major forums (including Google's YouTube Forum).  This therefore indicates that the problem might be your end.  Is it ONLY the YouTube app, or are others not working too - Can you test a couple?

Try these anyhow.

1. Unplug TV from the wall for 2 mins and try again
2. Whilst TV is unpluged reboot ISPs router
3. Considering you have the latest firmware, if steps 1 and 2 fail to resolve the problem, try a factory reset of the TV

Cheers