There are lots of fellow users here who have had, and solved, all sorts of problems. But they won’t be able to help unless you give them some info about history and configuration. Mostly this type of issue results when the underlying network is changed on an existing system, but until we know the background, it would just be guessing!

There are two initial steps I would try. 

First, wire a single Sonos speaker to your router with an Ethernet cable.

Second, unplug all Sonos devices from power, then reboot the router. Give the router a couple of minutes to reboot before plugging back in the Sonos devices. Wait another couple of minutes before testing.

But these are fairly generic suggestions. As @Antifon states, in order to give you a more calculated response, we’ll need a ton more information. 

Or, you could merely submit a system diagnostic , and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Hi

I can with a reasonable amount of certainty say that your issue will most likely be resolved if you assign a static/permanent IP Address to each one of your Sonos products via your routers DHCP page. Early on in my use of Sonos I had a similar issue until I assigned each product its own IP Address.

Most likely if your router reboots due to power “wink” or automatic upgrade it’s reassigning IP Addresses and some may be duplicates. If you are unable to make the IP Address assignments...then as suggested please provide information about your network:

• Most importantly what brand/model is your router or router/modem combo?
• Is it a single router and modern?
• Is it a router/modem combined?
• Is it a Mesh Network?
• Is it a network with range extenders not of the same brand as your router; nor provided by your ISP?

Providing the information may even catch the eye of a community member that has experience with your brand of network equipment.

Thanks for everyone’s help. I’m getting somewhere at least. Most has been resolved but still left with an issue. Sub woofer can’t be seen so I can’t add it to one of my rooms. I have tried following the advice but still getting nowhere 

How are you trying to add the sub? Before you can add it to a room you must first add it as a new product to your system. Afterwards the Sonos app will ask you where you want to assign it.

I’ve reset the sub, then reinstalled it and it adds it; however it doesn’t show up in my system, so when I try and assign it to a room, it doesn’t exist

If it is actually being added to your system it should show as an unassigned product. So you’re saying that if you go to a room and click add sub it doesn’t pop up as an available product? 

Are you by chance running two systems on different subnets and/or do have S2 and S1 as a split system? If the latter you gave to open the appropriate Sonos app on your device.

No it’s one system, the sub does come up as unassigned, but when I click on it, it doesn’t find it 

I’ve tried resetting again and still no luck

Have you rebooted the target room for SUB?