Assuming you have Atmos-capable Sonos speakers have you checked that the Spatial Music setting is enabled in the room setting? Settings>System>room>Sound

Yup, i just edited my original post to mention that the spatial music is activated. I do see the Atmos tag for other songs, just not with one which has both UHD and Atmos available. 

Do you have any rooms grouped with the Era 300? Any non-Atmos room grouped would restrict the stream to Ultra HD.

I don’t have any grouping with other non-atmos capable speakers or rooms. Just playing from a stereo pair of Era 300. 

I can currently play the track in Atmos to a stereo pair of Era 300s.

If you play the first 30secs, then rewind to the beginning of the track, does it stay as UHD?

Unfortunately, I’ve not come across a track not playing in Atmos when an Atmos version is available, so not sure of any obvious fix.

You may have to submit a diagnostic and contact Sonos Support to discuss. They will be able to analyse the diagnostic and hopefully uncover why the Atmos version is not being streamed.

@SnazzySnS 
The track ‘De Selby Part 2 by Hozier’ I searched and found on Amazon Music service via the Sonos S2 App and it plays as Atmos audio here on a stereo pair of Era-300s. I’ve attached a screenshot just to perhaps check if it’s the correct/same track you’re referring to?

That’s the same one I played @Ken_Griffiths 

@Ken_Griffiths 

So strange that it works on your system but not on mine…I can see the atmos tag in other tracks:

@SnazzySnS - do any of the tracks on the Unreal Unearth album play in Atmos for you?

Have you waited to see if the badge changes @SnazzySnS on the ‘Now Playing’ screen? Sometimes I’ve seen the App take a short while to update. Also maybe try closing/reopening the screen to refresh it.

I don’t think I’ve ever seen a UHD track change to Atmos mid-track.

If a track is available in Atmos it plays Atmos from the outset and the badge reflects that.

Unlike an HD/UHD only track after a speaker reconfiguration where it might take a minute or two for the badge to update mid-track.

Edit: I’m thinking it may be some DRM issue with the Atmos version, unless someone else from the US can play the track in Atmos on Sonos

Yes, @Mr. T, I guess it would make more sense, like you say, if that particular Hozier track was not distributed by the Artist/representatives in Atmos format in some countries/regions and only the UltraHD version had been made available under some kind of licence restriction/agreement, that might explain the differences seen.

@Mr. T - yeah the whole album plays in UHD. 
I don’t believe that it is a geographical restriction because I can play the album in atmos with Apple music via sonos as well as directly from Amazon music app. Definitely a weird bug ‍♂️.

My line of thinking was a specific DRM issue/bug for Sonos streaming the Atmos track (for some users), rather than an actual geographical restriction imposed by the Artist/representatives.

The other track you posted, Burn Alive, is available in UHD and Atmos, with Atmos playing correctly.

You’ve now confirmed the Atmos issue for Hozier relates to that whole album (with every track available in UHD/Atmos). At this point, I think only Sonos Support would be able to confirm why that is the case for you.