Playbar is compatible with S2. 

It sounds like you’ve already ventured down the factory reset path, so have another go at this. Press and hold the mute/play-pause button while applying power. Keep holding until the LED flashes amber then release. Once it gets to flashing green you should be able to re-add it. 

Thank you for your reply. It seems that the S2 app is the problem. It’s unable to recognize a compatible speaker which has been reset and is flashing green.

Have you tried deleting and reinstalling the Sonos app and rebooting your router and phone?

After repeating the same steps four times, the app finally recognized the Playbar. There’s a troubling element of randomness to everything Sonos.

Here’s hoping that this S2 hassle is worthwhile, and it solves the many problems I had under S1.

If you have had many problems under S1, it is extremely unlikely that they will be cured by S2.  My Sonos system has been rock solid for the 10 years I have owned it, and there is no “troubling randomness” about Sonos.  What you describe sounds like it is most likely caused by wireless interference.

If (when) your problems continue under S2 please come back on here or contact Sonos Support so that appropriate troubleshooting can be done.