Best answer by Ken_Griffiths
See the below info and links too. Take particular note that the router and any access points must be on the same WiFi channel. Some routers and devices may change their channel and auto-select a new one on reboot. If that applies in your case. I would fix the channel on your devices.
Warnings about using Access Points, Extenders and Power-line Adapters
"Networks using wireless range extenders are known to cause issues with Sonos systems that are configured in a wireless setup."
"Ethernet over Power devices (also known as HomePlugs or Powerline adaptors) as well as WiFi Hotspots are not supported by Sonos."
"If you are using multiple access points, make sure they are all set to the same 2.4GHz wireless channel."
Also, a warning message sometimes appears on the controller when attempting to group players hung off an extender. This can also be triggered by meshed WiFis. Grouping may still work, but potentially suboptimally.