App Continually Losing Connection with Sonos System

Have you updated your device, the Sonos app and checked for Sonos hardware updates in the app?

Have you made any changes to your network other than removing the Boost?

Do you have a Router/Modem provider by your ISP in use in addition to your Deco mesh? If so, an ISP update to their equipment may have triggered something as it sounds like you may have two active networks (Deco Mesh and ISP network).

First avoid the factory resets if at all possible, they rarely solve issues and delete valuable troubleshooting information that support can access. 

A simple network refresh is often al that is needed, power down ALL Sonos Reboot the router and power the Sonos back up. If you find yon need to do this often you can try to avoid the problem by setting static/reserved IP addresses using your router's DHCP Settings page. Power down all Somos, reboot router and controller and power the Sonos back up. 

You removed the Boost, did you also remove Ethernet from all Sonos? To go to Wi-Fi mode you want all unwired as an initial configuration.

Thank you both for your responses. 
AjTrek1 the Sonos app and hardware updates were done although some hardware did give issues with updates. Some took several attempts. 
I do have an ISP router and Deco Mesh. 
The main Deco is hardwired to ISP router and then feeds other wireless Decos around house. Sonos connected to network on Mesh. 
Stanley_4 I will try network refresh and power down as advised. I will also look to set static IP addresses as I have seen this often mentioned. 
I did hardwire one unit to my Mesh Main unit and the system seems to have miraculously reappear although response times are sometimes slow when controlling multiple units across the house. 
My current network is fibre optic provided with 750Mbps so speeds are fine. 
Thanks for your help. 
 

Sounds like you may have a double NAT issue.

Has the ISPs router been placed into bridge or passthrough mode? If not are the Deco units in Ap or bridged mode? I ask because you should only have one device handling routing on your network.

Hi Pools-3015,

I’d have to ring my network supplier (Truespeed) to find out as their main router is not one I can alter. 
I’ll check the Deco ti see what mode they’re operating in. Thanks

So quickly checked and Deco Mesh is is router mode so will change to AP and hopefully resolve. Would you still recommend static IP for each product?

I do recommend static IPs. That is the way I have had all the devices I need to find easily configured on my network. I configure the IP distribution to start at 192.168.1.50 for example. Configure static IPs between 192.168.1.1 and 192.168.1.49

You cannot have static IP addresses with Sonos only reserved.

I think many people don’t understand the difference between the term ‘static’ versus the term ‘reserved’ when used in networking. 

You are right! Should have used the correct terminology…

Reserve IP addresses for your Sonos speakers from your ISPs routers web page.

I tend to use "Static / Reserved" to try and minimize confusion. Most folks aren't network experts so simple and clear is good

Ddepending on your ISP router's abilities you might find you gain a lot by setting it to bridge/bypass/transparent mode. Different devices use different terms but what happens is the ISP router, for all practical purposes becomes invisible and your router takes over all the functions.