That seems odd…but power surges, especially when power comes back on are frequently odd. I’d try a reboot (unplug, wait two minutes, plug back in) your Sonos devices, which will force them to reload the OS and reconnect to your router. In fact, it might not hurt things to reboot your router while they’re unplugged, but I don’t think that would affect this particular issue, it’s just a good idea, especially if there has been a ‘surge event. It may have impacted the router, it may not.
Then do a test. Set up an alarm for five minutes later. Let it go off, and see if it bothers you works properly, and exists after you’ve quieted it. If not, I would recommend that you submit a system diagnostic within 10 minutes, and call Sonos Support to discuss it. But 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.