I have a Play:1 that I recently had to factory-reset after network problems. Although I've set it up again using both my Android phone and my Mac, the Sonos application loses sight of the device after setup.
It's connected to my home LAN and I can ping it, plus browse services on it using VLC - but I can't see it in the Sonos app.
I've tried setting it up using an Ethernet cable - this works, but when I move it back to the original location (which has good wireless coverage - I'm using my laptop from right next to the Play:1 now), it's not visible to the Sonos app.