I witnessed two issues related to the Sonos app:
1) As soon as I group multiple Sonos speakers together and play music (the Sonos speaker I assigned in the Sonos app is part of the group), the song text display feature on the LaMetric does not seem to work properly anymore: the song text display still gets triggered, but is blank.
2) Whenever the display of the song text via the Sonos app on the LaMetric is triggered, the current display cycle of the app that was showing previously gets reset to the start (e.g. the Netatmo app starts again at the very beginning with the first sensor). This is especially an issue in case of radio stations, which seem to trigger the song text display every 30 seconds or so, whether I set the app to "display at song change only" or not. As a consequence, I never get to see the data in the Netatmo app from my other sensors, as the app gets always interrupted by the Sonos app before getting there and then restarts at the beginning.
Regarding issue 1) it seems that this has been fixed in the meantime. The Song text display now seems to work flawlessly for me. Great!
Issue 2) is still persistent. @Julian: you are right, the song text display should only be triggered when the song information was actually changed. This is another issue!
About no. 1: It seems this only happens when using a Playbar in TV mode. Sonos wouldn't send any data in that mode so the Sonos app on LaMetric should simply ignore that and should not trigger a notification for empty song data.
About no. 2: What shall be done here is to only trigger a notification if the song information was actually changed. What happens here is not that radio stations are sending song info over and over again, it is Sonos that would periodically broadcast the info for applications to update their views. It is obvious that applications listening to the Sonos data traffic shall handle that internally.