After I upgraded my Sonos Ones (4 of them, 2 pairs) to S2 and downloaded the new app, everything was fine - at first. About 10 minutes later, the app gives the error message “Unable to connect to Sonos”.
I connected each of the speakers directly to my router (wired) and everything worked great. I gave each of them a static IP address. When I returned the speakers to their respective rooms and now connected to the network wirelessly, it worked fine for ~10 minutes. My iPad is on the same wireless network. Interestingly, I can play music on the speakers via my Amazon dots. Also, these speakers have been working fine for a couple of years without issue until I upgraded the app.