There was a problem with YouTube yesterday. It wasn't a Roku issue, as I had the same problems using my Shield players as well, which are Android based. It appears to have been resolved later in the evening, as I could again get into the players and watch content.
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee, just another user.