Just purchased an S2 and went through the setup. Paired with phone & Connect App on Android without issue. Also configured with 2.4Ghz hidden SSID and network test indicated successful connection. Then came time to use the scale. Nothing but problems. First the scale would not take anything but weight and when it did it gave the 'wearing socks' icon. Then when the final weight was attempting to register the scale indicated an unknown user with the big question mark. Reset the scale and attempted setup 2-3 times. Then I remembered the issue I had setting up my Forerunner 965. Hmmmmm.....
Some suggestions:
1) Must be 2.4 Ghz network.
2) Watch didn't like hidden SSID. Scale allowed me to use hidden SSID. Scale didn't work. Then used visible SSID. Scale started to work.
3) If readings don't show up on Connect App you may need to add 'Weight' to the 'At a Glance' widget. Click 'See All' if it doesn't show up on your home screen. If it doesn't from 'See All' you can click/hold and move it to the home screen area so it does.
There have been a lot of others having issues getting their S2 to work. My thought is maybe the above points will help someone. Particularly the suggestion to use a visible SSID. I'd suggest giving that a try and see if it fixes your issues. It did for me - at least for now. Good luck.