It will probably help if you explain what Sonos components you have in your system and how they are connected together.

It sounds as though you are referring to a Boost, but that is a product that was designed to improve wi-fi coverage. As far as I’m aware, it doesn’t play any part in adjusting the volume anywhere.

Having said that, I recall that some people reported no longer being able to see their Boost from within the updated app - but I don’t think that alone should be causing a lack of volume control.

The booster is connected to my Rega system which I used to be able control the volume. I have a playbar 6 metres away which is also wired. I connected my Sonos Router which I was told by Sonos Support that I no longer need it but thought it might help. It didn’t. I also have a play3 which is WiFi but nothing to do with the Booster. 
My Sonos App sees the Booster as Dining Room but I have no control. It says Line-in is disconnected & nothing highlighted for be to adjust/setup. 
Maybe a simple unplug all connections, reboot home router then reconnect all Booster & Stereo cables again.
I’ll give it a go 

Ok - the problem is that Sonos don’t sell a product called a Booster, so I’m guessing that this is a name that you personally use to describe it? It seems likely that it could be a Port, but I’m just guessing. Without knowing the exact product you are using and referring to as a Booster, it’s hard to give any advice.

But if it is a Port, then I believe that other people have experienced problems with the Line-In on that product with the new Sonos S2 app, and that Sonos are working on fixing the problem.

Sonos does not offer a “Sonos router” either, we’d love to help but we need the real names of the various problem bits to make any progress.

So sorry. It’s the Connect. 

There don’t seem to be many people reporting problems with the Connect and the new app, but that may be because (as far as I can remember) most of the Connects were not S2-compatible, and so won’t work with either the old or new S2 app. So there probably aren’t very many Connect users on the new app.

If you can see the Connect in your system, but can no longer see the Line-In volume control, that does sound like a problem with the new app. It may be worth contacting Sonos Support and checking with them that they are aware of the problem and are planning to fix it at some point - or they may have a work-around.

There may be other options - for example some people have downgraded their system to use the older S1 system instead, which might be a quicker way to get back to (roughly) where you were. Again, Sonos support should be able to advise on whether that will be possible with the equipment you have.

Thank you. I’ll contact Sonos