Yup - seems to be an issue with the home screen. Other aspects work and so do videos etc. 

eg. Watch History > video is playing fine.

Yep, can’t login on TV, and can only load playlists on phone which do play fine. 
Can search on playlists menu as well, which seems to search all of YouTube.

Airplay to TV is working from phone.

It’s working now.

It's not just YouTube packing a sad according to down detector.

Something probably went bang in a very important place.