Did you disconnect them from the Beam before trying the Arc setup?
Try powering the Beam down when trying the new connection.
Try powering down ALL Sonos rebooting router and controller then powering just the Arc and surrounds, add the surrounds first then add the Sub.
Try it the other way around if you still have issues.
Thanks Stanley. I got it to work when I disabled 5ghz on my home wifi network with the help of my internet provider.
