Im experiencing the same issue, no surround audio control. Can’t adjust the rear speaker volume without turning up my arc which is already loud and you can’t really hear the Era 300´s

I see the Surround options on my iPad controller App - see attached screenshot. Maybe try rebooting the mobile and signing IN/OUT on the controller App your using and see if that fixes the issue.

Also make sure you have updated your Sonos app to the latest version from the App Store/Google Play, as well as Settings - Manage - System Updates - Check for Updates.

Thank you! So I unpaired and repaired them to my arc and the settings came up! But strangely they work for music but when connected to the tv as source all the sound is only coming from the arc and nothing or very minimal is coming from two era300’s as rear surround. Even changing the sliders does nothing. 
 

what makes it even stranger is it seems to work a little better on YouTube but worse on Netflix? 

What is the Now Playing screen displaying for source?  Are you getting a surround format (Dolby Digital 5.1, DD+, or Atmos)?

If the audio coming from the TV is in stereo format, you won’t hear anything but ambient audio coming from the rear speakers.  Sonos doesn’t do any sort of simulation to create surround audio that isn’t present in the source.  If you select something in netflix, for example, that is specified as being recording in dolby surround or atmos, then you should hear audio from your rear speakers.  The Sonos app should also tell you what audio format you’re getting, but I’m not 100% sure that is still the case after all the app changes recently. 

Yes, the app tells you what format the soundbar is receiving. And as mentioned, don’t expect sound in the surrounds all the time. Stand by the speakers for a few minutes while playing something in 5.1 or Dolby Atmos and familiarise yourself with how often or infrequently those channels feature sound. It will reassure you.

This seems flaky in the app, comes and goes.

i use YouTube Dolby 5.1 demos to reassure me that all works correctly.

I would say it works very well for me, showing me 100% of the time with accuracy what is playing from the Arc, but I’d probably get berated for it...

I have seen several times when the app said 5.1 but there was no sound from the surrounds, switching to a test gave the expected sound there. I tend to suspect the source was broadcasting 5.1 but hadn't bothered to actually put audio on them, just the front stereo ones.

The next time I run across this I plan to also check the Sub and Center channels to see if they are getting any sound.

Eh? Broadcasting in 5.1 but “hadn’t bothered to actually put any audio on” the surrounds? It’s not something a sound engineer is or isn’t bothered to do. If audio isn’t mixed in 5.1, it can’t be broadcast in 5.1. As mentioned, the surrounds only kick in when that channel has ambient/relevant audio to contribute. It’s not like when you play music with the surrounds set to on ‘Full’.

i have only just got my first used playbar and sub, and it’s very disappointing how little 5.1 content there is, especially on the bbc iplayer, i always check sonos app to establish why surrounds are quiet, but sub works more often, maybe 2.1 ….

Yes, most terrestrial broadcasts are stereo (although importantly there is more 5.1 content to be found on the HD channels). The terrestrial streamers (BBC iPlayer, ITVX, Channel 4 etc) are not really the places to experience surround sound unfortunately - presumably there is a cost or bandwidth consideration to recording, mixing and streaming ‘normal’ TV in 5.1. Sonos’ home theatre is always best experienced with the subscription streamers, especially Apple TV, Disney+, Netflix, and Amazon Prime…

NB: I believe the sub is always in play, regardless of whether there is a .1 in the audio as it takes on the bass end of all content to allow the soundbar to deliver to its best potential across the other frequencies. But happy to be contradicted on this!

The sound engineer has full control of the content of each 5.1 channel and has no requirement to put sound on a channel just because it is present.

The times I noticed it may have been an error but it was clearly showing 5.1 while neither Surround was producing any sound. Flipping to a different program had the Surrounds working as expected so it is unlikely it was a Sonos issue.

I have never dug into the workings of the Sub with different signals but my impression is that it is sent the low frequencies for Stereo music sources and the .1 / LFE channel if present as in 2.1 and better sources. I haven't paid attention to Stereo TV signal sound enough to have noticed how that is treated.

Sometimes all I get in the Sonos app is the ability to reset surround sound distance. Other times I get the full volume controls for TV and music. 
 

sometimes switching content and then switching back to what you want to watch gets them to show up, but it seems very random in nature.

my best guess is that Sonos is trying to be “smart” by enabling and disabling this option when it thinks we should have it available, but bugs cause it to hide incorrectly. It would be nice if it was available the whole time that surround speakers are configured regardless of whether there is surround sound available or not because at the moment it just creates issues when it’s not working properly.