Hi @Whitney FL, welcome to the Sonos Community!

Is this when first setting up the system? If so, I’d recommend rebooting your router (turning it off for about 15 seconds before turning back on), rebooting each Sonos speaker when the WiFI is back online, and finally force-closing and then re-opening the Sonos app.

If this doesn’t help, mind letting us know a little more about the network? What make/model of router are you using? Do you have any wireless extenders in use? Are any of the Sonos devices connected by Ethernet cable?

Hi, I tried all of that.  Two speakers were new to the party.  When I went to add them I noticed my arc and two S-one disappeared from the network.  This is when problems started.  From I then hooked up arc to router and it worked and joined but disappeared an hour after removing it.  I would still get the photo above when trying to add it.  Then my kitchen and living ro which never disappeared through this went away.  At this time I decided to reboot every sonos product after unplugging router.  Each item gave me the notice above.  I waited a day and tried again.  Now ally Sonos one and sl ones are added but arc will not add. Gives me notice above.  I have 6 Sonos one, one arc and one sub.  This is not a cheap system and I am frustrated beyond belief.  I can listen to arc when plugged into HDMI but can't get surround.  

My wifi is through comcast I'm using their x1 system. I moved recently and it's all new equipment. I test over 100 Mbps.  

Got it, thanks for trying that. Sounds like the Arc may have ended up in a kind of "half set up" state - just to confirm is it currently showing either a solid white light, or no light at all?

If so, I’d recommend performing a Factory Reset on the Arc, and then in the Sonos app, as long as you can see your other speakers, go to Settings > System > Add a Product.

If you’re still having trouble, you can always reach out to the Support Team via either phone call or live chat - they have some more tools available to help you :)

I did try that and it will only add when the Ethernet cable is plugged in.  Any solution for that?

Understood - so the Arc appears in the app, with all of the other speakers, but only when connected via Ethernet?

In that case I would recommend reaching out to the Support Team - they will be able to take diagnostics of your system to get a closer look at what is causing this to happen :)

So this took about an hour over the phone with SONOS but ended up VERY helpful.  First off - they needed to separate my 2.4 and 5ghz wifi connections with different passwords so they don’t try to connect to the 5ghz  Then because of the type of router / modem from comcast they had to get into the advanced wifi settings and change 2-3 different things.  I’m honestly not sure exactly what it was - like i said, about an hour of troubleshooting.  At the end of the day it was extremely helpful they logged into my computer to do it.  Thank you SONOS!