Hi I’ve got a single router with Sky mesh using the SkyQ system. Sonos 2 App. I seem to have got the speakers stable on my iPhone now for a while but my IPad App still only shows one speaker. The Spotify app on iPhone shows all sonos speakers but on the iPad only the one (same as Sonos App). This suggests IPad issue perhaps?
Maybe try switching off ‘Private Address’ on the iPad - it’s located within the WiFi connection properties page in the iPad iOS settings/WiFi connection.
As you are using a Sky WiFi mesh setup - if you do continue to experience problems with your Sonos products you may find that wiring one Sonos device (only) to the primary Sky router may work better for you. It will hopefully switch all Sonos devices onto SonosNet, which is its own built in mesh WiFi and it has 3 available WiFi channels of its own in "Settings/System/Network” in the Sonos App. You could try each of those channels and get the Sonos system running alongside your Sky wireless, but running on a different channel and that might prove to be a little more stable… but perhaps see how things go for you and I hope switching off ‘Private Address’ works for your iPad.