This isn't something that's not already known, but I just wanted to share how all the problems I had with my Beam (plus two era 100 surrounds) very regularly disconnecting from wifi (BT router) went away when I set a static IP for the Beam on the router. It really wasn't difficult to do (once you access your router's admin page) and has been transformational in resolving this issue. If you're having this problem, I really recommend 'fixing' your Beam's IP as static not dynamic (DHCP). It has also resolved an issue with the Sonos app losing access to Amazon music - I think the Beam dropping messed up the app too.
(Note: As well as the Beam, I have 2x ERA 300s in another room and the 2x ERA 100 surrounds (on the Beam), but I didn't fix the IP address for any of these - I think the Beam needed it because it was on the busier 2.4 Ghz channel on the router and my other Sonos speakers connect to 5 Ghz.)
