After reading many similar complaints, I understood Sonos considers it is up to YT to fix the issue. I do not agree because I chose Sonos because it is YT compatible. If it is not compatible, Sonos is lying when they say they include the YouTube Service.
For my part, most of my playlists have missing songs, and some even have all the songs unavailabe!
I am very disappointed because the devices are very good, and the app is also nice.