In several threads, in the last few hours, Sonos has reported that they’re looking in to Alarm issues in the controller.

You may want to follow this thread, which appears to have some traction:

EDIT: reposted in another thread (linked above).

I am having the same problems after having disabled my alarms for one day, they do no longer show in the Sonos app. Also the app is loading very slowly. But when I add new alarms (after the app is fully loaded) it keeps forgetting the new alarms after a reload of the app.

Now I just checked my Sonos app on my macbook. There the (old) alarms are still available so I just enabled them. But after reloading this app, als here the alarms are gone. Waking up will never be the same again

My alarm did not go off today. Since the latest app update alarms disappear then reappear randomly in the app. I don’t think the Sonos team have a clue about what they are doing. 

My alarms are working again. I suspect the issue is on the server side. I had a similar incident about two months ago. I think it is best to never rely on Sonos as your only alarm. 

I think the issue are still being going on.

I too have had some strange alarm issues. Here is the weirdness that has occurred:

1. An alarm that has been set to a particular station but only the alarm tone is sounded. This has happened several times, all sporadically. Checking the settings for the alarm shows that it was set correctly.
2. Synchronization between my iPhone and iPad with respect to alarms has had several issues where a change that I have made on one device doesn’t appear on the other device. The sync issue doesn’t get resolved for several days resulting in confusion. Which device takes priority?

1. The chime playing is a signal that at the time the alarm is supposed to go off, the speaker (not your controller app) is unable to reach where the music it is supposed to play from. That could be local music, or a server that supplies the stream, it depends on where you’ve set the alarm to play from. Rather than skipping the alarm, the Sonos plays the chimes to warn you about the alarm, since it can’t, at the moment, reach where you told it to. 
    
2. The way I believe the way it is supposed to work is that any data gets placed on the system, on your speakers. That way, the controller, wherever it resides, can read the data and present it to you.

It sounds like there’s some communication issues going on locally, you may want to submit a system diagnostic from multiple devices, and call Sonos Support to discuss it. Don’t post the resulting diagnostic numbers 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.