Comment by tasty_freeze

Before when I said I had spent hours trying to debug this, I did exactly that. Turned off every single wifi device in the house, turning off every printer, phone, and the ring doorbell. I tried bringing up one sonos device at a time to figure to figure out if one of them was causing problems.

Also, I used wifiman on my android phone to sniff out other networks. Finally, I am lucky enough to live on 3.5 acres so there aren't any nearby wifi access points.

Anyway, another comment has pointed me to the apparent solution: the sonos bridge device apparently is not essential -- just connecting one of the speakers via a wired connection makes it the bridge for the sonos network.