Arc Ultra/sub4/ERA300 not playing dolby atmos

 Is “Spacial Music” on in the Room settings?

Yep, that’s on. I even tried switching it on and off a few times, but no change. 

 In the iPhone Settings - Music is this setting on?  Not sure that would apply to the Apple Music app in the Sonos app.

That’s also on

Same for me. Impossible to listen Dolby Atmos thru apple service thru Sonos S2 apps. even with setup always on.
I switch from Sonos ace + 2 eras 100 + 1 sub to Sonos arc ultra + 2 eras 100 +1 sub, Dolby atmos ok with Sonos arc, Ko with Sonos arc ultra !!!

I’ve got an Apple TV where I have Apple Music connected to the arc ultra. Dolby Atmos OK with TV HDMI + Apple TV + Apple Music with Dolby Atmos songs. But KO if I listen same songs from the apps Sonos with Apple Music. Grrrrrrrr

The Apple Music app settings don’t have any impact when playing from the Sonos app.

If you remove surrounds/sub from Arc Ultra, do you see the Dolby Atmos badge when playing to Arc Ultra as stand-alone device?

If yes, then add surrounds and see if it’s still available, then add Sub again.

 I’m not sure what’s going on.  I have the system Arc-Sub3-300s and I see the Dolby Atmos logo though it’s smaller than it used to be.

 OK… now I see an issue.  I have several Atmos playlists in Apple Music.  I just started one and the first track reported itself as Lossless.  Then I opened the queue and started another track which reported itself as Dolby Atmos.  After that I went back to the first track which then reported itself as Dolby Atmos.  I think the new app update screwed up how track formats are read.

So, I’ve just remove sub and the 2 eras 100 as requested, my arc ultra is standalone and no Dolby atmos…

Is any audio badge visible in the Sonos app?

I no longer use Apple Music, so can’t try this myself, however, with Amazon Music after any room configuration change, the audio stream recalibrates itself, which can take a couple of minutes, so let a couple of tracks play to see if the Dolby Atmos badge eventually appears.