Changing WiFi can be similar to a locksmith changing all the locks then leaving the new keys on the kitchen counter as he leaves. As household members return, they then find themselves locked out.

Whenever replacing the router it is important that you power down everything on your network, then restart in the following order:

router
Network switches, if any
Mesh points, if any
Sonos units
NAS drive, if any
everything else

Allow each step to complete before moving to the next step. As you have discovered is easier in the long run if you had given the new router the same WiFi credentials as the old router. If you haven’t done this reset yet, I strongly recommend that you do this now.

Finally, I recommend that you go into your router setup and “reserve” or “fix” IP addresses for all regular network clients, especially the SONOS units. This will prevent a variety of vexing future issues.

Yes, I know that this is a bit of a mess, but it is time well invested. The Community regulars have all done this and we don’t have issues from one decade to the next.

Now, with respect to SUB:

I recommend un-pairing the SUB, if possible, continue if not. Factory Reset SUB (only the SUB), wire it to your network, then add it to your system. Be careful to add SUB, don’t setup a new system. Update SUB if nessary. Now you can unwire SUB and add it to PLAYBAR.

Thank you but I have no idea how to reset IP address on my router. I have removed the S2 app because the other 3 products aren’t compatible even though I bought them at the same time. The Deco mesh system I installed changed the WiFi password, but I still have use of the original. Last night everything worked as long as I switched to the old WiFi system on my phone. The 3 non compatible products work on old app with old wifi address. But the sound bar can’t be found. It’s all become incredibly awful. The sub is not compatible ( according to the S2 app). I was forced to upgrade as I couldn’t get into my original app until I did. Sigh 

I don’t have an unpair option. Only delete sub. If I press the spanner option I get taken to an information help page. I’m not sure if the playbar is on the app. Find products doesn’t work. 

Sounds like you still have your original router and WiFi, and now a new Deco mesh WiFi running at same time?.

When I set my Deco Mesh I used my original routers SSID and passwords and turned the WIFI off on the router. 

Sonos found it straight away.

Ideally you need to return your Playbar to S1 if you want whole house system again.

Your problem seems to be your Sonos S1 speakers are happily running on original WiFi which is still going but you can only see them when you connect your phone to that WiFi network. 

Deco creates it's own WiFi network seperate from your original.

You can revert the Playbar back to S1 using the S2 app, it's a faf but doable.

Evidently, you have two routers, new and old, on the air. This creates chaos for SONOS. It’s chaos for other units too, such as a phone or TV, but this is less noticeable because they communicate out to the Internet. SONOS units need to communicate with each other and they will not tolerate a split network.

This is solvable, but I think that you would be more productive working directly with SONOS support. We don’t have access to the information we need to quickly guide you through this.

Both Playbar and every Sonos Sub manufactured too date are S2 App compatible, so not sure why the App is informing you it’s not compatible… there must be some underlying reason if you are seeing that ‘incorrect’ message. You mention you have two other speakers, but it’s not clear what they are, but if they’re Play:1’s (for example) they too are S2 compatible - so perhaps post back what they are before deciding to return your setup to S1, as @Keithmac mentions it’s a bit of a ‘faff’ to downgrade a Sonos device and I’m beginning to suspect you may not need to go down that route. 

Can you also clarify what Sonos devices are currently setup in "Family Room 2” and "Dining Room"… Also outline if you are using an ISP provided router/modem and if that device is either ‘bridged’ or operating in ‘modem’ mode, and/or if you are using the Deco mesh as your router/WiFi mesh?

I’m wondering if you may have setup the Deco mesh hubs ‘bridged’ instead? …and merely using them as WiFi access points. In fact the Deco mesh hubs might ‘possibly’ be the root-cause of your problems here, especially if you are perhaps using double NAT (two Router setup) …and moreso if you have two WiFi SSID’s broadcasting around your home, which are both accessible to your mobile controller device, and perhaps auto-switching between those two separate wireless network subnets. The same might also be the case for your Sonos speakers too, if you have accidentally misconfigured the new Deco mesh system with an existing WiFi router.