Hoping to get an answer to this problem. 

You should be asking Google, they control the syncing between the main YTM database and their SMAPI endpoint.

“YouTube Music” => “Library” => “Liked Music” shows all my liked songs. Where within Sonos are you looking?

For me, they show up immediately: if I like a song in YouTube Music then it’s there at the top of the list right away.

Note that if you like a song in YouTube itself (as opposed to YouTube Music) it might not show up on that list depending upon your YouTube Music preferences. To get liked songs from YouTube to show up in YouTube Music, go to “Settings” => “Recommendations” in the YouTube Music app and turn on “Show your liked music from YouTube”.

To edmountain: I’m talking about the list that shows in my Sonos app. For a year now, if I was on YouTube via my phone or laptop, and “Liked” a song on YouTube, it would also show up on my Sonos app on my phone under YouTube Playlist, then Liked Music. No more. The last one that shows up there is one I “Liked” on YouTube over two weeks ago. I have since “Liked” on YouTube two more songs, and they aren’t in my Sonos app under YouTube Music “Liked Music”. Thus, I can’t play the latest two on my Sonos speaker. 

I can’t figure out what has changed. 

 

I have asked google this: “why is syncing not occurring between what song I "like" on YouTube and what shows on my sonos app” . I get these ideas: 

• Internet speed:  I have fast internet. That’s not the problem. ]
• Check your music files  Liking youtube music has always worked before. I am not liking AIFF or Wav
• Update Sonos Music Library - go to Manage menu, click update music library now. Under Systems Setting, I see Your System on the left, and Manage on the right. When I tap on Manage, I see two things: 1) Music Library, when I tap on that, there is nothing there to update it. I tried to “Scan for New content. Nothing happens. I tapped on Detect Music Library. It shows nothing  2) System Updates. That is set to automatically update. I find nothing that says “update music library now”. 
• Check Audio settings It further states: An audio setting on your TV or source device might be processing the audio before it gets to Sonos, causing a delay. You can check your TV and source device's audio output settings, or disable extra audio processing. I’m not using my TV for this. I’m not sure what they mean by “source device”. I’m using my laptop or phone to Like a song on YouTube, which then fails to show on my Sonos app.

• Adjust your audio format: Some TVs and source devices use additional processing when playing surround sound audio, which can delay the audio. You can change the audio format to Stereo (or PCM) to remove this delay, but this will disable surround sound audio Doesn’t fit. 

• Bond your speakers: If you're playing music videos on YouTube, you can bond your One SLs or Fives to the Beam as surrounds. Grouping the speakers to the Beam can cause a slight audio delay. Don’t think this fit. 

Now below the above AI answers, I see this: 

Does Sonos app work with YouTube?

YouTube Music integrates seamlessly with Sonos, allowing you to play your favorite music directly on Sonos speakers. To link YouTube Music with Sonos: Open the Sonos app. Go to Settings > Services & Voice.Aug 16, 2023.   Okay, so I try to find Services & Voice under Settings. Find nothing like that in Sept. 2024. 

Still very stuck as to why the YouTube music I will Like has now stopped showing up on my Sonos app. Do I need to reset the App? I’m concerned I’ll lose what once was showing up, but doesn’t anymore. 

Also by the way, under Content Services in my Sonos App, it shows my Preferred Service as YouTube music, and Connected Services show YouTube Music with my personal YouTube. 

But alas, my Sonos app has stopped showing me what I “Like” in YouTube as of several weeks ago. 

@J.A.B. That's what I'm talking about as well.

When I like a song in YouTube Music, it immediately shows up on Sonos in the YouTube Music "Liked Music" playlist.

You keep talking about liking songs in YouTube as opposed to YouTube Music. Hence my suggestion to check your YouTube Music app settings to make sure your YouTube Music account is configured to acknowledge those likes. If your YouTube Music account does not acknowledge YouTube likes then there's nothing Sonos can do.

You know what, edmountain?? I went to the YouTube Music app, which I never had to use before to get what I “Liked” onto my Sonos app (until several weeks ago). And using that app now puts the music I want in my Sonos app. THANK YOU. It’s just weird that I didn’t have to use it before. But I’m happy now and you get the GOLD STAR. 

Excellent. Enjoy!