Make sure that the TV’s own speakers are muted.

Yeah they are as set up on my settings on tv as sound bar  so it only connects sound through the arc 

Did you set the surrounds and subs up using the correct method - i.e. using the “Add Surrounds” and “Add Sub” options in the Arc settings, rather than ticking them on the Grouping screen and pressing Apply.

Yeah it’s been set up fine months I brought the era 300s March time set it all up correctly. and it’s only now it’s sounded echo but doesn’t do it when I watch sky or when I play my PS5 maybe it’s Disney plus as both things I have watched on Disney plus it echos. 

Just to be 100% certain, on the Sonos app, when you tap on:

Settings - [Room containing Arc]

and scroll down, you see the option to “Remove Sub” and “Remove Surrounds”, and another option for “Surround Audio”, with a menu showing TV level, Music level, Music Playback etc? 

Yeah they are all listed etc remove subs, remove surrounds. I did see somewhere that u remove surrounds and re add them and it should be ok. I did have an issue when I added the era 300s to my set up. So I rang up support and they went through it step by step. Been fine all this time done a update last week and now I can here echo on some things I watch 

I would definitely remove the Eras as surrounds and re-add them to see if that helps return them into sync when playing Dolby Atmos on Disney+.  

Should only take you five mins to find out.

What model TV do you have? Are you using the TV’s native Disney+ app or are you using another streaming device?

I have a Sony A90j I mainly use the app on the tv rather than the app through sky