Media Player Entities, their volume levels, All speakers, and Spotify

Okay, I’m confused.

I have:

media_player.spotify (Software integration)

media_player.kitchen_speaker (Google Home)
media_player.living_room_speaker (Google Mini)
media_player.guest_bathroom_speaker (Google Mini)

I also have media_player.all_speakers

If use Spotify to control the music volume it syncs perfectly with the Spotify media player integration. As a result of Spotify being connected through Google, I’m able to choose “All Speakers” inside of Spotify.

When I do so, and I set the volume to 100%, for example, media_player.spotify jumps the volume attribute to 1 as expected. The all_speakers media player jumps to 1 as well. One of the Google Mini devices goes to 1, but two of them read different values below 1.

I’m not sure what this behavior is all about.

Is there a volume level syncing issue with multiple media players?