Sounds like something is going on with your local network, not really Sonos. 
 

Have you tried connecting a single Sonos speaker (not a Sub or Surround speaker)  to your router with an Ethernet cable? Or called Sonos Support directly to discuss it?

Hey Airgetlam,

No, I haven't tried Ethernet yet (need to locate a cable first..) and haven't reached out to Support directly, figured I’d try this route. I've experienced issues with the Arc for several days now, despite my surround functioning properly for about a year, one speaker lost its pairing after sound would go in/out (it still works, just became unpaired). When I attempted to resync, I couldn't establish an internet connection. I understand that the immediate guess might be network-related, but to my knowledge, nothing has changed. Would that impact the ability to access the iPhone app? 

Best,

N

‘Nothing has changed’ is something that is frequently incorrect. Certainly, nothing has changed from your perspective, but unfortunately, there’s no guaranty that a neighbor may have set up a new router that’s causing wifi interference, or that a router firmware update has been pushed to your router without your knowledge, or even MS Defender has pushed out a new definitions file which breaks all Sonos connections. Or any of dozens, perhaps other things I’ve not mentioned. Networks, despite our best intentions, are not ‘static’, and Sonos, which lives on the network connection, is perhaps more sensitive to changes than most, due in some part to not only the need of each device to communicate with the controller p, but also with each other, something most LAN connected devices do much less of. 

So, without much information about your particular system, I’m starting with the basics, in particular a wired connection to a single Sonos device, which normally forces all other devices to connect to it, in a ‘SonosNet’ or ‘wired’ situation. The next step, assuming you’ve not attempted a factory reset (very bad, and erases all sorts of data that may complicate things, and annoy you) is to check for duplicate IP addresses, something which can be handed out by a router which is in a ‘bad state’, frequently exposed due to the fact that when Sonos does a software update, the devices reboot, and ask for fresh IP addresses. If what they are handed by the router are ‘bad’, that needs to be fixed. 

Much of this would be much easier for a Sonos rep to see in a diagnostic, something I don’t have access to. But there are many users in this forum that understand Sonos, and networks, that are willing to help. I’m just one of many. 

As has already been suggested, don’t Factory Reset anything without further consult.

Mother Nature is never fair, you could have a hardware issue. 
 

We can’t help unless we have more information about your network and SONOS system. Give model numbers.