This is an odd one.  I just installed a mesh system.  All connectivity is fine with Sonos and other devices.  All speakers work via Sonos app, which I never use as I use Alexa.

Alexa is acting odd.  With the speakers that have Alexa integration, I can ask a question like what is the temperature and I get an answer, so connectivity is fine.  If I say play radio station x or band y, she says she will play it, but she does not.  I can play these sources via the app to the very same speaker.

I have two older Sonos speakers which are connected to Amazon dots.  On one of them, Alexa will start and stop music when requested.  On the other, she will start music, but not stop it, when requested.

I cannot think of anything else to try and resolve this as I can’t see an obvious root cause.