I’m seeing the same, in that www.youtube links to playlists fail in their onebox whereas removing the www makes it work. My digitalocean server is in London. The same is true for my Hetzner server in Germany.
Both of the types of links onebox OK on this server (meta.discourse).
So it does look like a Europe thing.
https://www.youtube.com/playlist?list=PLWVQAe9fXZolICdfMjY4MNdYdMgTOx5QT
https://youtube.com/playlist?list=PLWVQAe9fXZolICdfMjY4MNdYdMgTOx5QT