TV: 42PFL6007/T12

The general YouTube app menu works, but once I select a video it only buffers some 10s and then (despite the play button being active (i.e. the pause button is visible on the on-screen-control)) nothing happens - simply a black screen.

Have reinstalled youtube app, updated the app, restarted TV and restarted internet. Still doesnt work.

What is wrong? How can I fix this?