I recently bought a new wifi router/access point an ASUS RT-AC88U
Once I switched over to it I found that I had sporadic access to my Sonos speakers (Play 3, Playbar + Sub).
Sometimes I could connect to the speakers, sometimes I couldn't. When I could connect I'd sometimes be able to see all the rooms and other times only 1.
I played with a bunch of wifi settings and finally tracked down the culprit.
Wireless menu >> Professional Tab >> Airtime Fairness
This setting is enabled by default. When I disabled it my access to my Sonos was restored to it's former fully functioning glory.