Android fails to transfer to Cast Speaker Group, but works on iOS and web player

[Brian--]

I have a Pixel 9, and transferring music from the Spotify app to one of my Cast Speaker Groups fails ('House Speakers'). This works fine on my wife's iPhone and the web player. It also works on my phone when I cast to a different Cast Speaker Group ('Master Speakers').

I also use the Home Assistant SpotifyPlus integration which uses the developer APIs, and I notice that this integration fails to list this paritcular speaker group (but has no issues showing the other speaker groups). The raw data from the integration shows some hex garbage in the speaker list.

I also noticed that the Web API through the 'Try It' button on the Developer Dashboard fails to list the full set of devices shown to me in both apps and the web player:

I then created a new speaker group with the same speakers, and that new speaker group works. After creating this new group, I also noticed more corrupted hex garbage in the device list produced by the Home Assistant SpotfyPlus integration. I've filed an issue (issue#186 on GitHub) with the integration's author to understand if the problem is on their side, or if the problem is on Spotify's side. Given that I see this problem also on my Android phone, my guess is that there's an bug in the Spotify server code? Or perhaps in Google's integration of cast speakers?

Feel free to talk nerd-speak with me, ask me to collect extensive debug logs, etc, as I have 20+ year career as an embedded software engineer in many disciplines, lead a team in a top tech company, and am currently working in the media + devices domain (over 5 years in this role).