It sounds like the PC has some kind of power-saving setting that is ‘possibly’ interfering with the connection to your shared music library, so I would start with exploring the Windows power-saving features.

Also check the network adapter and HDD properties in the Windows device manager to see if there are any power saving options there too and disable those, if applicable.

It’s possible aswell that some System tasks, like disk defragmentation, or similar, are also scheduled to run when the PC is not logged on/being used ..and that something in the task scheduler might be interfering with the streaming connection. 

So perhaps try exploring those type of things and switching them off one at a time (or re-schedule some tasks) and see if that (hopefully) resolves the alarm issue.

I’ve thought of that, but if it goes to sleep/loses power so that sonos can’t pull the music off it, sonos normally just plays the chime instead. The PC is set not to sleep as well. The music also plays fine if I hit the play button after the alarm fails, so it seems to be getting hold of the music ok.

Just curious, but if you were to set a second alarm, say ‘one minute’ after the first, does that second alarm then work for you?

I’m just thinking the first alarm may wake up whatever device was in power saving mode and the second alarm will then play - if it does (consistently play), then it’s just a case of finding what aspect of the setup is in some kind of power-saving mode. 

This morning for example, there was a second alarm set 20 minutes after the first that worked fine. It’s not a fair comparison though, as the second one was a chime alarm. Generally though, if it’s asleep the alarm doesn’t wake it up, it just failsafes to the chime instead. The oddity is more that it’s pulling the alarm playlist, but not *playing* the alarm playlist.

Perhaps try the ‘second alarm suggestion’ with the exact same playlist and just see what happens. If it does work (consistently), it might infer something is in power-saving mode in your setup and then take it from there.

I’m assuming of course that if you set the alarm to work now, whilst the PC has just been used and is fully awake, that the playlist is working for you.

Another thing to perhaps also try is setting an Alarm using a Sonos Radio station, or some ‘other’ connected source as a comparison, just to see if the matter is ‘perhaps’ just related to the PC shared library connection.

An update. It appears that the chime resets whatever playlist is playing back to the start. It could be the case that I Just Slept Through the musical alarm and only noticed the chime, before gaslighting myself into thinking the music didn’t play at all. Previous cases can be explained by a wifi failure making the chime play instead. I’ll update if this turns out to be more than that. Thanks for the help!