Are you able to hardwire one of the Arcs to your router? Even if its temporary to get things setup properly, then you can connect them wireless again.

I have found that having my main speakers, Playbar, Arc and Amp hardwired, I have not had any connection issues. But many have also had success with a totally wireless system. 

It is worth exploring what works best for you though.

I can try to hardwire a single speaker, yes… Although that is still frustrating because it’s one less speaker I have in use around the house… The router is in my basement electrical room.

I will try that and see if it works.

Only needs to be wired for a few minutes and then can go back to the normal spot.

Endless trouble with exactly the same issue. It eventually connects and works, but rarely use the app now and just rely on Spotify and Google home to connect to Sonos as they find my speakers within milliseconds. 

I have had same issue in past month where according to Mac desktop app all products are fine and dandy, iOS app all products don’t exist. I have had to start using the desktop app instead now (same WiFi network)

I have the same problems and occur frequently.  I am so fed up. Their service Center sucks as waiting time to connect to their staff is 80 mins.  Who would want to wait this  long.  
 

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Same. System not found 80% of the time. I’ve updated the app everytime it’s been updated… I reconnect every few times in hope that might fix it. Our house is silent these days as cant’ be arsed to go through the pain of trying to get music playing through my £200 speaker. :-(

Right. 
I suffered the pain of taking all my speakers to the router and connecting via Ethernet. Then factory resetting them in turn and adding them back to the system… each took ages. But…

the system is now working far better. 
the app boots and finds the system within 2-3 seconds so problem solved.