I would first try a full reboot of your Unifi mesh system and see if that solves the issue. Ensure you have the multicast settings enabled as below (taken from another thread here in the community):

• From the Unifi Network Application interface, click on the Settings icon from the left side menu.
• Click on the Network tab. 
• Select the network Sonos is connected to. Click on the Default network name if there is more than one. 
• Scroll down to Advance Configuration, and click on Manual.
• Check IGMP Snooping and Multicast DNS. 
• Click on Apply Changes and allow up to 3 minutes for the settings to update.

If that still doesn’t work perhaps wire one standalone and working Sonos device to the primary Unifi Hub/Router and let the speakers switchover to SonosNet (All devices will show as WM:0 in the ‘About My Sonos System’ area of the App) then try the Playbar setup again from factory reset.

Give it a few minutes post setup and then see if all will then run on your Unifi signal when you uncable the standalone speaker from the primary hub/router.

Hope that helps to resolve the issue.

Indeed, I did try those router settings from early searches on this board. 

I also tried connecting the playbar directly to the router but run into a catch-22.  The playbar won’t connect to the app if ethrnet is connected….so can’t do the setup. And the app doesn’t seem to see the newly reset playbar if it is on ethernet….so again can;t do setup.  Tried enabling mesh networking too, to no effect.

 I am now going to try creating an independant SONOS vlan to see if that works.  (not feeling optimistic)

Weird since this all was working unitl I simply changed the IP’s.  The network architecture has not changed.  And I was able to register 6 out of my 9 devices.   Frustrating.  

Did you try my suggestion of wiring a standalone ‘working’ Sonos device to the primary hub and switching all over to SonosNet …and then setting up the Playbar from factory state?

Well I solved it.  Just created a seperate VLAN, stuck all the SONOS devices on it and boom….all worked

Of course now the problem is that I cannot control sonos from the app or desktop unless I am on that SONOS VLAN.  Even though routing works (I can ping from main wifi network to the SONOS).  Always something...

Yes, all the Sonos devices and their controllers too, need to be on the same Subnet.

created a port/ip group of the gear on the sonos net and tried a simple “Allow All” rule between that and the main network.   Obviously missing something as it does not work.

Well, got it al working.  Not exactly sure how but I did turn on mDNS on both the main network and the VLAN.  The phone Sonos app now works from either the main network or the Sonos VLAN.  The last remaining is the desktop app.  That won’t work unless on the VLAN but aat this point I don;t care too much.

Frustrating day.  Set up Sonos ERA 300 for my wife and then added a Gen 3 sub.  Simple to set up and liked it so much that added a set to my work area.    Again, simple setup and sounded really nice.  Added a second ERA 300 and the effect was truly enjoyable.  So decided to take the last step and add another sud.  Well, struck the rock one too many times.  It has turned my system into a nightmare.  Can’t set up the second sub.  Then issues with the first sub.  Not Registered shows up for the sub and no way to connect it.  Tells me incompatible software and no way to get past that roadblock.  Am thinking about tearing my entire system down and starting over, but not sure if that would help.

Any suggestions for getting my new Gen 3 sub (and now my old Gen 3 sub as well - the message from it is that it is not not registered.  Another roadblock.

Refrain from Factory Reset of any SONOS units without further consult.

As a first step force close the SONOS controller. Nothing critical is stored in the controllers.

The Sonos controller?  You mean the Sonos app?  Have done so and same issues.  Reset app and rediscovered existing system.  Got the initial sub back but new 2nd sub still won’t allow assignment to any room.  Connected, but “Not assigned”.  When click on that it asks to let us add a sub to one of the rooms.  When that continues it says that a compatible Sonos speaker is required to add Sub.  Below that is a circle with an exclamation point in it.  When I hit Done I go back to the Sub issues “Not assigned” menu.  Blue circle next to the Issues: Not assigned menu item.

Me again.  I am wondering if I have inadvertently found my answer.  

“You can’t add two Subs to a stereo pair.  You can only add two Subs to a Home Theater room.”

I am trying to add a second sub to a room consisting of a stereo set of ERA 300s with one sub, not a Home Theater room.  If the old post (7 months ago) I located is correct, I have my answer.

Thanks!

None of these solutions worked. Tired factory reset. New dedicated network. Hardwired option. Product refuses to register to my account no matter what I do.