Again, do not Factory Reset anything at this time.
Better safe than sorry. If things seem to be going off the track below, stop and seek comment before creating more mess.
Due to its age and unrelated to the S1/S2 mess, you could be experiencing some issues with BRIDGE. Let’s power it down and set it aside for the moment.
Going forward do not follow any instructions leading to S2 -- regardless of any promises of improved this or that. In my opinion the notices about the benefits of S2 are much too aggressive and, as you have discovered, can lead to a mess.
Make sure that the S2 controller is uninstalled from all of the devices used to run the controller. Wire the PLAY3 to your network. If it wants to update, go ahead. Now the PLAY:3 should be fully functional. Stop here if it is not.
Next, let’s see if we can get BRIDGE online. Power it up and wire it to the network. If it wants to update, go ahead. If it does not request an update it may come online without any overt notices -- this is good and means that BRIDGE is likely working normally. Let’s verify this by going to Settings → System → About My System. Here both BRIDGE and the PLAY:3 should be visible. If BRIDGE is not working, power it down and set it aside.
Even if BRIDGE seems to be working, let’s power it down and keep PLAY:3 wired to the network. This is a precaution because a faulty BRIDGE can result in difficult to describe, intermittent issues that have nothing to do with S1/S2.
Now, and only now, Factory Reset the PLAY:1. Don’t Factory Reset anything else. Add PLAY:1 to your existing system as if PLAY:1 is a new unit. (Take care with this step because it is easy to follow the wrong branch and setup a new system) Again, do not follow any suggestions to “improve” your system by installing S2.
Hopefully PLAY:1 will install without event and you’ll be good to go. PLAY:1 will probably request an update (reverting to S1) and this is OK -- just avoid S2.
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Now, about that BRIDGE. By now you can imagine that I don’t trust it and you are correct. I assume that you are using BRIDGE because you don’t want to permanently wire any of the other units to your network. If you can easily wire another unit to the network, I suggest that you retire BRIDGE now, or keep it under very close supervision if you continue using BRIDGE. In the future if you continue with BRIDGE and are experiencing any odd issues with some or all units dropping off, suspect BRIDGE until proven otherwise.
While I prefer wiring one or more SONOS units to the network, you can configure the units to use WiFi and at that point BRIDGE will become baggage. For now, let’s ignore the WiFi option and not introduce any potential for more drama.