Okay, it seems that this has been resolved, but I posted the topic in case anyone else runs into the same issue.

I uninstalled the Android S2 app, and then reinstalled from the Play Store. When I launched the “new” app, it asked me to press the ‘connect’ button on a speaker, which I did. The app then went into the same thing as my original post (need to update...yada yada). However this time when I went to the Play Store at the end, the options were Uninstall or UPDATE.

I selected UPDATE and then the app worked as it should. It found my system and was able to connect my S2 components.

Same here. Insane, that Sonos locks you out of your own system until you update the app...

I've got this issue as well but your solution does not work for me, so Sonos have effectively locked me out of my system.

Stuff like this is why so many users have a love/hate relationship with Sonos. My system works (or it did yesterday, and nothing has changed at my end) but I cannot use it. Guess I'll be spending my morning on the phone to support, thanks a bunch 🤬

Well, well, well, minutes after I posted this a new version of the S2 app became available on the Google Play store (although the stated release date - September 13th - is a total lie). I guess someone at Sonos towers forgot to push the button before locking all their users out. Bravo, idiots  That's half an hour of my life I'll never get back.

Exactly the same happened for me. App was claiming to be up to date with a release date of September 17th, suddenly update available and now it has a release date of September 13th….. Guessing someone messed up an update and it’s been rolled back…. 

Seems to still be an issue. 
On Android, still getting the update app, even after an uninstall and re-install. When going to the Apps store only offered unistall or open. No update GRRRRRR!!!!!

IOS is fine thank god.

Update I’v now just been offered the update.   What a P.I.T.A.

Note that Sonos supplies the update to the various stores (frequently different ones for different locales), but has zero control over when those various stores flip the switch on when the update becomes live. Which makes life somewhat difficult for both us as users, and Sonos as a company.
 

I’ve done this dance before as a software release manager, trying to coordinate each individual platform and locale is, shall we say, ‘fun’. Or not so much fun, really, just frustrating, as much as it is frustrating for the end user. 

My understanding was the same as Bruce.  It would be nice if Sonos could implement some sort of grace period, where the firmware on the device can be ahead or behind version compared to app for 48 hours or so, till everything is in sync.  I’m guessing this was considered though, and possibly introduced more problems than it resolved.  You don’t exactly want to spend time developing and testing for a scenario that will happen for a fraction of your customers over a short period of time.

Sonos might have no control over when updates are released, but they know when they have been released. There's no reason they can't wait until the update is universally available before effectively bricking users' systems.

If you live in an area where the app update seems to always trail behind the firmware update, you could just turn off the automatic firmware updates.