Has your router received a pushed update? Have your neighbours changed their router causing their wifi to conflict with yours? 
I’m not dismissing your problems; I am questioning your assumption the “blame” rests with Sonos. 

Do you run your devices with fixed ip addresses? This has resolved many folks’ problems - including mine of more than 5 years back, resulting in many years’ trouble-free operation. 

No I don’t run fixed IP addresses. Did set that up when I had the problem with a wired sound bar but then started the whole system again from scratch when I started running entirely wireless and didn’t set it up again because I appeared to have solved the problem.

Has my router had a pushed update, possibly. Every other device that uses it is still working though. Have my neighbours changed Wi-Fi? Doesn’t look like it. On 2.4hhz I’m on my own on channel 9 and on 5ghz alone on channel 43.

All of which kind of underlines my point. Sonos is supposed to be a ‘it just works’ solution that I could recommend to my parents in law not something you have to dig around Wi-Fi or router settings for and it just isn’t any more.

I could even understand your suggestions if all my devices were consistent and showed the same results but three devices showing different combinations of speakers (a second android device shows the same as the Pixel in my photo) suggests something odd going on.

It suggests IP conflicts, which would cause some devices to see only the devices which they are not in conflict with.  Common occurrence.  As to “it just works”, Sonos hasn’t used that marketing blurb in years, it it was in comparison to Squeezebox, where the marketing blurb was “Just load the latest beta, that might fix it.”  Not a high bar to clear.  Unfortunately since then, networking has become far more complicated, and far less robust.  Mesh routers, multiple access points, pods, etc. meant for single point reliability sometimes wreak havoc on a system which needs to constantly communicate between devices.

Anyhow, reserving IP addresses will prevent any IP conflicts in the future.  I can count on one hand the times this did not alleviate, if not completely cure problems like yours.  Make sure you do a network refresh first to clear out any existing duplicates. 

This is an unfortunate choice because channel 9 interferes with channels 6 and 11. Use channel 1, 6, or 11, not “Auto”. Also, set the 2.4GHz band for 20MHz channel width.

Well you kind of are dismissing the problems - and I got the same reply as I have the same issue all the time. Simple fact is Sonos does not work as well as it used to and whereas once I was a firm believer in all they did I could not recommend them anymore and if I hadn't spent as much money as I had in having multiple speakers all over my house I would not do it again. The iOS app constantly says no music is selected when music is playing and there is simply no point trying to see what song I am listening to becuase by the time it registers what song it is the song is over. I have deleted apps, updated, rebooted router all the usual rubbish that I never ever had to do before and the only conclusion you can make is that it doesn't work as well as it used to and nothing seems to be done to correct it. Very annoyed.

I’m not the only person to suggest setting fixed ip addresses. You don’t say whether you’ve tried that: have you? In many posts on the forum, it has been found to cure these problems.
Be sure to fully reboot your system and router first, so everything is running on clean addresses. 

A distributed music system, such as SONOS, requires more robust network support than simple email, web browsing, or video viewing. Most routers in otherwise “perfect” networks are inept at preventing duplicate IP addresses while things are updated or not rebooted in the proper order.

Many of the regulars in the Community, myself included, were struggling with their SONOS system until they reserved IP addresses. At that point the struggle ended.

Describe your network for us. Which model router are you using? Are there any WiFi extenders or mesh points? Which SONOS units are in your system, are any wired to the network?

Networks are more complicated now than in previous eras. Formerly there may have been a computer and phone on the network. Now there are multiple computers, Phones, TV’s, cable boxes, thermostats, light switches, SONOS, video cameras, WiFi access points, voice controllers, and more. Routers and network controllers have not yet worked out the details of managing all this without adult supervision.