https://www.theverge.com/2018/4/2/17190282/youtube-channel-pages-down

If you’re seeing a 500 internal server error while visiting YouTube today, you’re not alone. The company confirmed via Twitter at 2:27PM ET that channel pages were down, though individual videos could still be watched.

YouTube initially said that the error was only affecting some channels, but it’s since pulled a tweet with that clarification. There don’t seem to be any channels that are still up.