Alarm Issues for Multiple Sites

Not much we can do, unfortunately, as the public, we have no access to the hard data in the diagnostics. 
 

General advice might possibly be useful. First, there shouldn’t be any crosstalk between sites, even if they’re connected to the same Sonos ‘household’. Each ‘system’ would be separate. Second, try moving your ‘alarms’ by one or two minutes, either way. Frequently, if at the moment of an alarm is supposed to connect, the speaker can’t reach the server that it’s told to, and instead plays the ‘chime’, so you don’t miss the alarm itself. Third, in each location, I’d suggest a full network restart, to ensure these ‘ghost’ alarms, whatever they may be, are properly flushed. Unplug all the Sonos devices in that location, then reboot your router. Give the router a couple of minutes to come back up, then plug back in your Sonos devices. Give them a couple of minutes to boot up and reconnect, then open your controller and check your alarms. It should only show (and react to) the existing alarms.

Finally, continuing to work with Sonos, if none of the above helps, is recommended. They have access to the data in the diagnostics that we don’t. Given the odd nature of your issues, I’d encourage you to get through to a human, in my experience, the Chatbot isn’t always as clued in, yet, for the odd circumstances of your issues. if you’re not happy with one CS rep, there’s no shame in calling back a second time, and reaching someone different. While I’m sure they try to do equal training, there’s always someone who has a better understanding of the situation.

Worth reading this thread, too. A good explanation from a Sonos moderator about time shifting, and why:

Bruce, we did go through those troubleshooting steps, including talking to an agent.  We are dealers, and these are all separate client sites with no connection whatsoever.  I’m fairly sure this is a bug related to a recent update.