A few weeks ago, Google made YouTube Playlists work on Google Assistant devices. While it's great that I can now request and listen to YTM playlists on my Nest Hub and minis, it broke being able to play playlists from YouTube music on all of my Sonos devices.
Sonos One:
"Play Lady Gaga" -> "Playing Lady Gaga on YouTube Music" (= no problem)
"Play Current Favorites" -> "I also need to know which device to use"
"Play Current Favorites on the Bathroom Speaker" -> "Sorry, I can only play videos on devices using Chromecast or on cast enabled devices"
Nest Hub
"Play Lady Gaga" -> "Playing Lady Gaga on YouTube Music" (= no problem)
"Play Current Favorites" -> "ok, your youtube music playlist called Current Favorites. Here you go" (= no problem)
Nest Hub with Sonos Play:1 as default speaker
"Play Lady Gaga" -> "Sure, Lady Gaga from YouTube Music. Playing on Bedroom Sonos" (= no problem)
"Play Current Favorites" -> "I can't do that here but you can ask me to do that on one of your other devices"
Summary:
I can play songs and artists from YouTube Music on any of my devices (Google and Sonos) using Google Assistant. But I cannot play any playlists as soon as I evolve Sonos (neither when "speaking to" Sonos One, nor when telling GA on a non-Sonos device to play it on a Sonos speaker).
Judging from the response ("can only play videos...") I think Sonos believes songs and artists on YouTube Music are "music", but playlists may be "videos", which it then rejects to play. Just to confirm: my playlist does not contain any videos.