So check this out. I wasted the better part of this last weekend troubleshooting our Sonos speakers at home. Good times. Honestly all of the thousands of $$$ spent on these things…  was so close to all winding up in the dumpster/landfill.  
I recently upgraded our home network to Ubiquiti from a Chinese mesh platform. Generally works about 1000% better, but with the mesh we had the option of putting a puck near these speakers and connecting with a LAN cable. Now we are 100% wireless. I followed all of the provided steps to remedy, but no matter what I tried devices would not add back to the system even after a factory reset. 
 

Until I realized that one old play:1 was connected with ethernet. Once I pullled the cable out of that guy everything was fine… minus some minor issues. My question is now “why the hell is this a problem?” They were still all on the same network and I would like to be able to hard wire some devices to reduce the number of wireless clients for performance reasons, but I’m afraid to mess with it now. (I’ve worked in IT for about a million years.) 

Maybe the more obvious reason is “why isn’t that provided as an option to try along with the other 10 things?”  Unless I missed the one article containing it… I never saw it and it would have saved me hours and a lot of hair lost.