I’m unsure why casting from the Amazon app would fail, but if you’re after the best quality you should play via the Sonos controller app.
I use Amazon on the Arc with sub and it drops after Maybe a dozen songs.
Annoying and says '...failed to locate some required info....' or similar msg
Then it comes back up couple mins later. For the price would hope this works better..
Amazon usually works fairly well playing from Amazon.
What you are describing sounds similar to an error I saw for the first time earlier today. It cleared with no action on my part after a few minutes. I’m thinking it was an Amazon glitch, not Sonos as I haven’t changed anything here lately.
There is an Amazon / Sonos glitch that has been around for a while where it looks like the music in your Room is playing but there is no sound. If you add another Room to your current Room your current music will still be playing there. Un-group your current Room from the new Room, re-group and your current room will start playing again. Un-group the other Room and you are back where you started.