Sonos AMP disconnects from WiFi when adding as surround to Playbar also on WiFi

That’s odd, I can’t think of a reason why the Sonos Amp would disconnect…it should just do the process of adding the speakers as surrounds. 

One thought…you’re using S2 on this PLAYBAR, not S1, correct? Both the sound bar and the surrounds do have to be running the same OS.

Have you submitted a system diagnostic within 10 minutes of experiencing this problem, and called Sonos Support to discuss it? What did they suggest?

Oh…there is one more thing that I should have picked up on. You say both devices are on WiFi, and not Ethernet, but they are in two different rooms. When the Amp switches to ‘surround’ mode, it moves to a 5Ghz connection directly to the PLAYBAR, ignoring its connection to your WiFi signal. Is there a chance that the Amp can’t directly connect to the PLAYBAR, due to distance or obstruction? Try, at least temporarily, wiring both devices to your router with an Ethernet cable, see if the process completes then. 
 

Edit: ​@Mr. T beat me to it ;)

The connection between the TV connected device and surrounds is low latency, but it is not buffered much, so it cannot reliably go through walls and floors and is meant to be used with both devices in the same room. 

Thank you both.

The distance is almost certainly the problem then - unfortunately the wiring for the speakers runs to a different room 60 feet and many walls away.  I did not realize that the Playbar sets up it’s own 5ghz connection for surrounds - I did not see that documented anywhere.  I assume this is different than SonosNet.

I will plan on trying wiring both of them with Ethernet Cable.  I’ve been trying to avoid doing this as I just moved to a Unifi system, and I read that the recommendation for Sonos on Unifi is to use either all Wired (not an option), or all wireless (apparently won’t work for me due to distance).  I guess I’ll just try ethernet for these 2 speakers and see what breaks.

On a related note, if I move the Playbar and AMP both to ethernet, can I keep the sub currently connected to the same PlayBar as wireless, or does that sub then need an ethernet also?

There are arguments about what ‘SonosNet’ really is. I consider it the WiFi equivalent of a connection to your router’s WiFi….but not including surrounds, since that isn’t a ‘mesh’ like connection like SonosNet is, in my mind. Others include a wired connection from the speaker to the router (which makes no sense to me, that’s just Ethernet). But recently it has been suggested to me that the code team at SonosNet has different ideas about it than I do.  I stand by my definition ;)

As long as you don’t turn off the WiFi/radio function in the controller for your PLAYBAR, it will still connect to the Sub via the 5Ghz channel, even while your surround signal goes to the router and is sent to the surrounds via Ethernet.