Hey Davian, have you linked your Spotify account with the Google Home app? That's usually the issue -- Home can't use the service if the metaphorical door hasn't been unlocked by linking properly. Try "unlinking" and relinking? Or try clearing the cache for the Home app and Spotify app and try relinking. Hopefully, that will clear it up and you should be good to go.
So the next thing to try might be to restart your wifi network, and reboot the speakers. I'd also log out of Spotify -- I don't use it so you'll need to do what's necessary to accomplish that. Reboot the phone and then log into Spotify again. It's possible a Spotify update went awry or didn't complete.
If Spotify is showing as the chosen default music service in the Home app sounds as if the tunnel out to Spotify by Home/Nest couldn't be completed, so it defaults to YT Music. Assistant and assistant on Nest speaker devices aren't identical, therefore the fact that it works on one doesn't necessarily mean it will works on the other they are different processes, don't ask, lol.
Sounds to me Nest is knocking, Spotify ain't answering and Nest says, you get what I have. But that's just a guess.
I'm having this issue as well. "Hey Google, play music" always defaults to YouTube music on my 3 different nest/home speakers. I've tried delinking Spotify and relinking, setting to default again in the home app, restarting the speakers and the Wi-Fi network. "Hey Google, play music on Spotify" works as expected no issues, but without specifying Spotify, it defaults to YouTube music, so it's not an issue with being able to connect to Spotify it would seem. I'm sceptical that this has been deliberately setup to push people into YouTube music.
First, thank you GothamNY for trying to troubleshoot this issue. I appreciate your help.
Hello DavianM and DemomanCA,
Thank you for your post. I'm sorry to hear that you're having issues with your device playing the incorrect default music provider. I know it can be a frustrating experience when your device doesn't work as you'd like.
In order for the team to look into this issue further, I would sincerely appreciate it if you sent in feedback using the keywords,"GHT3 Music not playing from default" from either your device or the Google Home App. You can check out this article for more information on how to do so.
In the meantime, I recommend casting your audio from an app on another device to your speaker as a temporary solution as we try to resolve this issue.
I appreciate your patience as our team looks into this further and I'll keep you posted as more information becomes available. Feel free to continue sharing your feedback or any updates.