It happens only with my Chromecast speakers. The other endpoints I have tried are the Huawei P20 phone, the Samsung Galaxy Tab S2 8’’, a Dell laptop and a desktop PC , and I can play music just fine from all of these. The Huawei could play music even when it couldn’t cast it to the Chromecast speakers.
I have read the guide you linked and enabled ‘multicast routing’ on my Asus router, hoping it will help.
Thanks!
I would have never though of that because the setting is in the IPTV tab, and I don’t have any IPTV service enabled (my broadbrand provider offers it but I’m not interested).
The Chromecast speakers support only 2.4Ghz, but so does Sonos anyway.