Just wondering if you have multicast ‘device discovery’ issues across your network that’s preventing the controller device from communicating with your Sonos speakers. See attached re: SSDP/mDNS.

Such communication failure can occur across networks that use WiFi extenders, EoP adapters, or if managed switches are misconfigured. It can also happen if some settings on a local router are incorrect, or there’s software running on the mobile device that is getting in the way of the multicast communication, such as security software, VPN client, firewall, site blockers etc.

I’d perhaps investigate further in the areas mentioned and if still no luck then it maybe best to reproduce the issue(s) seen and then immediately submit a Sonos system diagnostic report from within the Sonos App, note it’s reference and contact/chat with Sonos Support Staff via this LINK and see what the Staff can perhaps suggest to help you to resolve the matter.

I was having general networking problems with Sonos which I may have finally solved. I was piggybacking one Sonos Port to another before going to my main switch to cut down on long runs in my networking cabinet, but that was effectively putting some Ports on a different network switch and that is a no-no according to some Sonos documentation I found. Eliminating that network piggybacking and plugging each port into the main switch directly seems to have made things perform better so far. 

I've had good luck running one Ethernet to the Sonos location then adding a cheap/dumb switch there to split out the differernt devices. 

As a plus it gives you a full speed connection to the switch, then whatever the devices can support, piggyback limits the whole string to the slowest device's speed