Are the players using the same Spotify account/login credentials - if they are, then it’s expected behaviour. Simply use one of the other family accounts in the car, or for Sonos playback. If the playback is two separate/different family accounts, then I suggest you raise the issue with Spotify CS.

Just for your info; here’s how to add multiple Spotify family account credentials to your Sonos system…

https://support.sonos.com/en-us/article/use-multiple-accounts-for-the-same-music-service