Which Sonos speaker is giving you problems? Maybe a Play 1 or Sonos One?
Factory resets usually make thing s worse, very rarely better so now you have to recover from that as well as the networking change.
If you have other working Sonos, power down the non-working one and connect to the others and verify all is good.
Power up the non-working one and see if the mobile Controller can find it and add it back into your existing system.
If it can’t try hooking an Ethernet cable from your router to the problem speaker to get past the setup stage.
https://support.sonos.com/en-us/article/sonos-led-lights
https://support.sonos.com/en-us/article/connect-sonos-to-a-new-router-or-wi-fi-network
