Stumbled across odd behaviour, wonder if anyone else has seen this.
I have 4 Sonos units, and everything up to date at v9.0.1. All my Sonos boxes are on and playing music. My iOS controller thinks I have 4 Sonos zones. My windows 10 desktop thinks I have 4 zones. My other windows 10 desktop thinks I have only 2 zones (but play/pause controls all the zones, even the ones it doesn't know about). I got into this situation by briefly switching off a Sonos box.
I have gone through switching off everything, re-booting the router followed by turning on each zone. I reset the confused desktop controller app instance. I even reinstalled it, and it still sees a very different Sonos network from the one in my house. I assume it's not firewall-related as the controller app can control the Sonos.
Any ideas for how to fix things?