Sometimes adding the Sub last can be a pain. Try removing your surrounds, then add the Sub before you add the surrounds again. You may also need to connect the Sub to your router with a cable.

Yep. Tried all of that.  No dice.  It's the update required to the sub that I can't get past no matter what order, what's connected, etc.  The update fails every time,   usually from the fix it screen as the sub adds not registered cause it cant run the update.   

How about removing the app, restarting your phone then reinstalling the app?

Do you have a PC or Mac? Install the app from the Sonos Support website and try again?

Yep. Still nothing. Tried an android,  an ios and a pc.   

Maybe try a bit different fix? Go to your router’s DHCP Settings screen and assign every Sonos device a static/reserved IP address. Power down ALL Sonos devices. Reboot the router, clearing the DHCP assignments. Then power your Sonos back up so they can pick up their new (and stable) IP addresses.

Try the update after doing this and see if it works. If not Ethernet connect the Sub to your main router’s Ethernet ports and give it another go.

If this doesn’t work I’d call Support back and give them another shot. Have your previous notes available and you might even shoot them a fresh diagnostic before calling.

I can't chg my router as it's supplied by my isp and locked out to me.   

ISP got involved.  They separated the devices.  They can see the sub poll the Sonos server and the download starts.   Then it fails.  It's definitely the sonos server, software and or hardware.   Even level 2 can't figure out a fix. They blame my network which it's not.  

Perhaps try a different local network - you could even ‘temporarily’ use a mobile WiFi Hotspot just to complete any updates. If it works, then you can look closer at your own local network setup.