Hi.  There is no such thing as a Sonos 1 speaker.  Nor a Sonos 2.  There is no such thing as a Sonos 1 app.  Please would you try and explain the problem more accurately?

I have the Sonos 1 App loaded on my phone. To confirm that I did not upgrade to the Sonos 2 App, I will point out that the the Icon for the App clearly says Sonos 1.

I have a Play 1 speaker, and a Connect Amp, and a Play 5 speaker.

I know that the Play 1 and the Connect Amp are not compatible with the Sonos 2 App. But they should certainly still be compatible with the Sonos 1 App.

My Play 5 does work. 

I deleted the Sonos 1 App and re-installed it, but that did not fix the problem.

I hope that this clarifies the issue.

@plshelpme, According to your profile, you have …

• Play:1 (S2 compatible)
• Play:5 1st Gen (only S1)
• Connect:Amp (depends on manufacturing date)

https://support.sonos.com/s/article/4786?language=en_US

In the S1 app go to 'Settings → System → About my Sonos System', is the Play:1 being displayed there?

Yes. And under Sonos OS, the Play 1 says S2

My Play 5, which is working, says Sonos OS: S1

@plshelpme, You split the system into S1/S2.

Is this process reversible?

While we don’t recommend downgrading your products to S1 after updating to S2, it is possible to downgrade by resetting the S2 products to their factory settings and adding them to an existing S1 system. An existing Sonos product running S1 software is required to downgrade an S2 product back to S1. Note that all settings and preferences will be lost when downgrading a product from S2 to S1.

 

https://support.sonos.com/s/article/4845?language=en_US

Thank you, Smilja- I will weigh my options.

I don’t know how it got split, but I suspect that I unknowingly downloaded S2 when I received a routine-looking notice that an update was available. I think that the first update notice didn’t indicate that it was actually an upgrade to S2. I would hate to think that this was done to trip us into bricking older equipment.
My Connect Amp is five years old and cost about $500. I understand Sonos’ need to move onward and upward with technology, but I hope that the routine-looking update notice was an error that won’t be repeated.

I am experiencing the same thing. I have no intention of splitting my “whole home audio” system into two systems with two apps. All of my products are S1 compatible, but somehow the S2 firmware made it onto the compatible products, rendering them incompatible. I did not even have the S2 app installed. Rolling back the firmware is very time consuming for the six or seven products affected. 

In theory, you can revert S2 products to S1 - providing you have at least one S1 device in the system. In theory, you factory reset each device. 

However, as I said in a reply to another thread, I have one Play1 that WILL NOT factory reset to S1. If Sonos Support manage to make this happen without replacing the device, I will update this comment! Please wish me luck…