Have you considered following the actual instructions?

https://support.sonos.com/en-gb/article/connect-sonos-to-a-new-router-or-wi-fi-network

Nice one John… I hadn’t thought of that! Course I followed the instructions… it didn’t work. I’ve had to manually connect with a Ethernet cable, dark ages! 

This is how I have had my system setup ever since I owned my first Sonos product, and what's funny is, this “ancient” way of networking has given me trouble free use of my now 11 speakers!

There are ethernet ports on all soundbars, Amps and Ports for a reason. Its to help when you have WIFI interference or some other issue with your wireless network. So go ahead and leave your Beam plugged in with its WIFI turned on so that your surrounds and Sub can connect to its private WIFI.

That “dark ages” solution still works for many, and obviously works for you too…

EDIT: The easiest thing to do would have been to use the same SSID and password as your old WIFI. Devices would have automatically connected.

The wired connection need only be for one device and then only temporary.   A wired connection triggers Sonos' proprietary mesh network, and is necessary to enable data to flow between Wi-Fi and SonosNet. In fact, networking wad surprisingly advanced in the dark ages.

Your original post contained no evidence that you had followed the instruction article.

I just unwired all the Sonos I had wired and things are working as well or better than ever.

I also find the limited diagnostic information we can see more useful in the unwired mode.

Not saying there aren’t times the wires are the best solution but today I’d sure give wireless a fair trial before trying wired.