I created a Standard test account and an Administrator test account on the Mini. I logged in to each account and opened Music. I downloaded some songs and started playing them.
In both of the fresh test accounts, engaging the Visualizer disconnects Airplay in exactly the same way it does when I am logged in to my everyday account. That is, Airplay connections and the local headphone output are immediately stopped when the Visualizer is engaged. At that point the Visualizer display appears to be 'stalled' i.e. not responsive to musical cues, even though the audio meter icon next to the song playing is active and the progress bar under the song title is advancing.
Once sound output is dropped, only the headphone connection can be reconnected without restarting Music.
This behavior seems to be consistent whether the audio file is local (downloaded) or streamed (Apple Music Radio e.g.)
When I was closing Music in preparation of switching to a test account, Music did throw a 'quit unexpectedly' error.
Thanks,
M@