That seems odd. Have you submitted a diagnostic, and called in to Sonos?

I’d be tempted to do three things, in a specific order, since, at least to my knowledge, data about the alarms is stored on the Sonos speakers, and not in the controller itself.

First, I’d power cycle the speakers themselves. Then, I would power cycle the router, and finally, I would power cycle the device that your controller runs on. I would expect one of those things to do the trick, as you’re ‘clearing’ old data from each device, and forcing it to reload its OS.  

These actions did nothing.

Ok, then I’d reach out to Sonos Support directly to discuss it, including that  system diagnostic I mentioned.