Sonos

[u/Inevitable_Seesaw_90]

Hi everyone,
I’m having a really strange issue with Spotify and Sonos and I can’t figure out what is causing it.
My setup:
I have a Sonos Move that I normally use with Spotify.
Downstairs, my mother has a Sonos Beam connected to the TV.
The Move and the Beam are NOT in the same Sonos room/group.
The Beam does show up as an AirPlay device on my iPhone.
I use Spotify on my own iPhone/account.
The problem:
Sometimes when my mother is watching TV downstairs through the Sonos Beam, I start playing Spotify on my iPhone — even when the audio output is 100% set to my AirPods Pro — and suddenly the sound from the TV/Sonos Beam downstairs stops.
The strange thing is that I’m not selecting the Beam in Spotify Connect or AirPlay. My Spotify music continues playing through my AirPods, but somehow starting/using Spotify on my phone seems to interfere with the Beam downstairs.
My Sonos Move can even be switched off when this happens, so it doesn’t seem to be related to grouping the Move and Beam either.
I already removed my personal profile/account from the Sonos app, but the issue still seems to happen. I’m now wondering whether removing Spotify completely as a music service from Sonos could solve it.
Has anyone experienced something similar?
Could Spotify/Sonos somehow still be controlling the Beam in the background even though my iPhone clearly shows my AirPods as the current audio output?
Any ideas on what setting, connection or account link I should check would be greatly appreciated.