For instance, when Sonos Radio HD was introduced, I was unable to play a full track without the audio dropping. I stripped my system back to a single One wired to the router. The dropouts continued. I can’t recall exactly what setting i changed in the router, but I was able to resolve the issue, which didn’t reoccur when I connected back the rest of the system.

I am not familiar with TP-Link, so I think you need someone with a working Sonos/TP-Link Mesh setup to chime in, I recall there are a few on forum, but may not be reading this, especially at weekend.

The App seems to have some basic info about connected clients:

https://www.tp-link.com/us/support/faq/1593/#:~:text=You%20can%20check%20detailed%20information%20about%20any%20connected%20client%2C%20change%20its%20name%20and%20type%2C%20enable%20Mesh%20Technology%20and%20high%20priority%2C%20set%20a%20profile%20to%20manage%20its%20online%20activities%2C%20and%20more.

​@IanJShaw 

I use a TP-Link mesh in Access Point mode, and Sonos works well.

Do you have your mesh nodes in Access Point mode, rather than Router mode? I think you do from what you wrote. 

On the Deco app, under More, then Advanced (where Operation Mode will say ‘Access Point’), ensure you have Smart DHCP turned off so that only your router is assigning IP addresses. 

Thanks ​@Rhonny . Yes, they're definitely running as APs.

You're not alone in feeling frustrated—many users with large, mixed-generation Sonos setups report similar issues. While Sonos officially states that all S2-compatible products should work together, the reality is that mixing older and newer hardware often leads to reliability problems, especially with syncing and control delays. 

Sorry for the thread necromancy but I’m posting this in the hope that anyone who found themselves in my position finds it helpful.

Short version:  I took out some of the older players and now my (smaller) system IS more responsive.

Longer version:  I’ve had a couple of “rooms” that have been problematic for a while.  One of the things that they had in common is that they were both pairs of Play: 1’s.  Some of the behaviour that could be expected of them included losing sync, refusing to join groups, refusing to change volume etc.  I took those out of the system by disconnecting them completely and waiting for them to be “forgotten” from the list of players in the app(s).

After a couple of weeks of monitoring, my system is much more responsive overall.  There’s still a short lag in syncing players when starting a Spotify playlist but it’s much shorter than it was before.  Far fewer instances of unresponsive or laggy groups.  And not a single “meltdown” (every so often a group would freeze and then spontaneously de-group with no music playing anywhere).  I haven’t made any other changes to Wi-Fi infrastructure or environment.  And I have replaced one of the troublesome rooms with Sonos One’s sitting in exactly the same spot that the Play: 1’s were in.  So I’m assuming it wasn’t the wireless environment that was completely responsible for their behaviour.

Google tells me the Play:  1 is nearly twelve years old.  Maybe this is confirmation bias in action but I think my original thesis is, at least, partially true for me.  Of-course it may just be the reduction in number of players in my house.  Or that my house is particularly wi-fi unfriendly and that a mixed system including older players would work perfectly in a cleaner environment.

However, if you find yourself in the situation I was in, and you’re mixing players across multiple generations, AND you’re in the financial position to be able to attempt this experiment:  you may get some help from disconnecting the older players and seeing what happens.

Thank you everyone who replied to my original post and suggested exactly this.

Sonos has recently stated older speakers, like the Play 1, will not get new features because of the older hardware used, though unlike the S1/S2 split they will still function on an S2 system. This could make room for changes on those older speakers’ firmware to make them work better - though Sonos hasn’t said anything about that…….

As I stated in my initial post, Sonos have previously publicly acknowledged issues with older players in systems.

It’s therefore not surprising that removing or replacing older speakers would lead to a better experience.