If I were to guess, I suspect your daughter’s  phone is connected to the Sonos via Spotify Connect , whereas you (might be/are) connected via the Sonos controller. Or possibly vice versa. Spotify Connect stays ‘connected’ until broken, even if the device leaves the WiFi.

The easiest way to ‘break’ a Spotify Connect connection is to play a different stream on your Sonos device. This will break the Spotify Connect, and allow one person using the Sonos controller to use the Sonos. 

I have the Sonos app on my phone. 

We are both using Spotify connect. 

The problem is that it also switches if my daughter is playing YouTube, Plex or some other media. 

Then my Spotify Connection is broken and it starts playing the media sound from her phone. 

It seems it is always switch to a new phone, it there is media playing, instead of what one would expect, continue to play on the existing connection 

Which is why, as I suggested in my post, you need to ‘break’ the Spotify Connect ‘connection’ by playing any other stream on your speakers. 

As far as I’m aware, Spotify Connect has no idea that the Sonos controller is installed or not. It is merely making a connection from the Spotify stream on your device to the speakers, without any checking to see if there is a Sonos controller or not. 

You might want to submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Ok...

I'm not sure I understand how you mean... There should be some setting to turn off any auto connect, but there doesn't appear to be any. 

We tested with my wife's phone and that can "take over" the Move as well, but it doesn't do it automatically. 

My daughter has the Sonos app too, so it's both on my and her phone. 

You’re asking me about Spotify Connect’s software. You’d need to ask Spotify. They control their own software, having implemented the Sonos ‘connection’ API themselves. 

No, sorry if being unclear, but it's the other way around.

Spotify Connect is playing on the Move. As soon as media (video through YouTube or Plex App, or Spotify) starts on a phone with Sonos app installed, that phone high jacks the Move and starts playing the media sound. 

Then I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Make sure the Move isn’t grouped to other Sonos speakers. 

It's not... 

Does your daughter you’re Airplay? Not sure if a this would overrule a connection that is in use, but it seems strange to me that a Spotify Connect connection would also be used for YouTube.

No, it's not... 

Let me try and clarify. 

Both my daughter and I have the Sonos app and we run Android. 

I listen to the Move through Spotify Connect.

My daughter is elsewhere in the house and she starts YouTube on her phone. Then Sonos app is connecting her phone to the Move, breaking my Spotify Connect.

She's not connected through Spotify Connect, but the Sonos app is high jacking my Spotify connection.