Problem with Spotify - Sonos connection since upgrade

Hi all and happy new years,
I have a strange problem that I seem to have traced back to a recent FP4 upgrade and I wonder if others face the same. I already submitted the issue to support but am also posting here as I could not find any trace of this issue for Fairphone anywhere else (but for some other phones OPPO similar issues seem to have occurred):

I am now on FP4.TP20.C.087.20231122 but the problem might have started with the previous update as I did them shortly one after the other.

I use Spotify to cast music to several Sonos speakers (IKEA Symfonisk). This works through two apps, either the Sonos app directly or Spotify. The direct Sonos control continues to work fine, so I can start and stop music from there, including from Spotify. But for about 2 weeks now, Spotify no longer detects the Sonos speakers, so when I go to spotif’s cast menu I see my Chromecast but no longer the Spotify speakers.

Looking through the forums of both apps, the suspected cause for other cases was the upgrade to Android 13. And indeed on my partner’s Fairphone 4 which is using the same WiFi (dual channel, connected to 5Ghz) and exact same (latest) app versions for both apps, but which is still on FP4.SP2K.B.089.20230807, everything continues to work just fine.

Maybe there was a breaking change on the API or similar? Anyone experiencing similar casting/streaming/general API issues?

Many thanks!