Couple of things. First, post the number of that diagnostic here, so the Sonos folks can find it, and know what they’re looking for in it.
Second, when a chime plays instead of a linked station/file, that’s a pretty good indication that at the moment the alarm was set to go off, the speaker was unable to connect to the stream. Rather than just fail completely, it fails over to the chime, so you’re still woken up.
Failing to make the connection to the stream is likely due to one of two causes. First, and most prevalent, is simple wifi interference . But it can also be caused by duplicate IP address issues. Simply resolved, albeit potentially not permanently, by unplugging all Sonos devices from power, then rebooting the router. When the router comes back up, plug back in the Sonos devices.
But those two potentials cover most, not all situations. Let’s see what Sonos says, when you post the diagnostic number.