If you changed the WiFi network the PC is connected to, which seems likely, you need to make sure that network is marked as Private. If it is marked as Public then the windows firewall will block all the important data.

my PC with the windows controller is wired and on a domain. the only thing thats changed is moved from S1 to S2. It worked perfectly fine on S1.

Sounds like a firewall issue then, as the S2 app has separate firewall settings than S1. I would compare them both. If using the standard Windows firewall then it should be configured for you during Setup. If using another one then manual steps may be required.

Not a firewall issue. makes no difference if i turn the firewall off.

After some investigation using wireshark i found some additional ports that S2 windows app was using. Added them to the firewall and allowed the ports to talk across vlans. weirdly the s2 app on ios and android worked without me need to do this.

When you first run the windows s2 app it tries to connect to an existing system but it would never find my speakers. I joined the windows PC to the vlan where the speakers were located and then loaded the app and connected to an existing system. which it found. I then changed the PC back to the other vlan. It was no longer asking to connect to an existing system however it still couldnt find any speakers.

I then noticed on my router/firewall igmp proxy wasnt allow multicast packets between vlans, even though it was working fine with the S1 windows app. a quick reboot of igmp proxy and it started working.

Next hurdle was getting the sonos media library to work, that required some more firewall ports, from memory it was 136-139,445 and 3445. also on the firewall rule i needed to specify the remote subnet where the speakers were located.