As a guess, the speaker is sometimes having trouble reaching out to the SiriusXM server to reach the content. Rather than skip the alarm, it’s playing the chimes. So what probably needs to be done is figure out why the alarm process can’t always reach the servers. It could be a rejected connection request, with the server being overwhelmed at the moment the speaker is reaching out, or it could be your local network not allowing the speaker to reach out, for some (random) reason. The next time the chime plays, instead of SiriusXM, within 10 minutes, I would submit a system diagnostic , and, when you can,  call Sonos Support to discuss it. Don’t post the resulting diagnostic number here, they get sensitive about GDPR.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

It also might be worth shifting the alarm by a minute or three to either side of 7AM, at least as a test. That might identify if the servers at SiriusXM are being overwhelmed by connection requests at that particular moment.