After you did the Factory Reset you options are really limited.
I’d try powering down all your Sonos, rebooting the router and powering back up only one Sonos to use to add the Connect back in with. Then power up the Connect.
Second try would be hooking it to your main router with Ethernet and see if it will rejoin using that.
The flashing green is normal at your stage.
The Sonos product is powered on and ready to be set up. It has not yet been configured or connected to a Sonos system.
If your Sonos product is not brand new, a flashing green light means that the product was reset and is ready to be set up.
I hasd already connected to ethernet. Just flashing green. Had reset as a result of Sonos support chat. erHv, left powered up learnt ad tis morning worked fine!Just need patience?
Might have been an IP address issue, which is what the power down / reboot cycle solves. Overnight was likely long enough for the normal DHCP refresh to kick in and sort the IP addresses.
The only good way to avoid it happening appears to be assigning static/reserved IP addresses to all Sonos from your router’s DHCP settings page.