This is normally down to one of two issues:  Poor broadband speed or duplicate IP addresses.  Please see this article: Tips & Tricks - Resolving random issues impacting Sonos devices... | Sonos Community

Ok ill look at this thanks. Broadband speed is 100 gb so can't imagine that's it. 

It’s actually LAN speed that is the concern more frequently than broadband speed. Sonos lives in your local network, so it could be the speed of their connection to your router, and not the router’s connection to the outside world. But the links provided are accurate. 

Thanks Bruce. 

I am going to reboot router and and speakers afterwards and see how that goes. Would like to get it sorted before adding anything more to system. 

Sorry, I meant connection speed! Thanks Bruce :) @Airgetlam 

With so many devices, perhaps allocated all around your Home, I would also personally recommend you consider running them on SonosNet, if not doing that already … the difference in the connections and how the setup works are explained in this Sonos Support document:

https://support.sonos.com/s/article/3235

If opting for SonosNet (wired) mode, I would also suggest doing the following:

• Set the routers 2.4ghz WiFi to a fixed ‘non-overlapping’ channel 1,6 or 11 and choose a 20MHz channel width
• Set the SonosNet channel in “Settings/System/Network” so it is at least 5 channels away from your chosen router channel.
• Remove the WiFi credentials from the "Network/Wireless Setup” in the App as those are not needed when running on SonosNet and it will stop your devices hopping between SonosNet and your WiFi signal.
• Ensure all Sonos products, particularly the wired one is at least 3 to 4 feet away from other Wireless devices including the router and other access points.
• Consider adding the Sonos IP addresses to the routers DHCP reservation table as that too will improve stability, particularly during updates and reboots of the local network.

Hopefully those few suggestion will assist to prevent audio dropouts in ‘party mode’… I also recommend checking out these two ‘hopefully’ helpful links too:

1. WiFi Interference
2. Wireless Interference Video: Wireless Interference and Sonos

Wow, alot of detail there thanks Ken. 

That's lockdown Monday sorted. 

I have a sonos connect that is wired so I'll try your additional suggestions.  

Another ‘small’ tip in that case - the more modern Sonos products apparently have ‘improved’ WiFi adapters by all accounts, so some in the community here, suggest using a standalone ‘more-modern’ Sonos device as the wired ‘root bridge’ device - so that’s something else to maybe consider for lockdown Tuesday perhaps ...ha ha  

I v an arc coming next week which will replace my connect so maybe that may be the option there. 

Thanks for your help 

Of I go with the wired option does that prevent the speakers from been used on Alexa? 

No, a wired connection has no bearing on Alexa at all, but I would maybe look towards a standalone Sonos product rather than one that’s perhaps regularly processing TV and bonded surround-sound audio - I opted for the Sonos Boost some years ago, as it was designed for that purpose, but I know some suggest devices like a Sonos One/One SL. There’s no harm in wiring more than one device to the LAN too. 

Perfect 

Thanks for all that.