I know this is a bit of an old topic, but i’m going to post anyway 
I’m experiencing the same issue as mentioned above. My Sonos devices keep going unavailable and I just don’t understand why.
My HA installation is running in a docker connected to the host network. Port 1400 is open if I scan it. When I reboot HA, the container, the Sonos devices report their status for a couple of minutes and after these minutes they become unavailable again. No logs, nothing.
I added, based on the solution per this topic, my devices to the yaml files, this action adds a line to the log: Automatic discovery is working, Sonos hosts in configuration.yaml are not needed. So I might as wel delete them again.
I know of some kind of ‘master’ Sonos device within the network, how can I figure out which one this is and can I change this? Maybe the current master is a wifi device and I have some wired sonos as well. Might make more sense to designate them as a master. But can’t find anything about this either. Might even mean I mix things up with other systems. I just don’t know what to look for.