Index S2 does not recognize me

Having the same issue here. Me and my partner use the scales. I have removed him and added him again via email and this time made sure that his weight when signed up was exactly the same as it showed when he was coming up as a guest. When I weigh myself it lets me tap through each of our names. However, when he uses it, after syncing his new invite, it only shows Guest? and when he keeps tapping it just shows the same Guest? icon. 

Hello JayLDN!.  Sorry for the delayed response.  Please try the following:

1. Remove the 2nd user (your partner)
2. Invite them again
3. Make sure they complete their profile completely after accepting the invite.  Do not skip any fields in the profile completion.
4. Attempt weigh in and profile selection by tapping scale after weigh in.

See applicable FAQs below:

Adding or Removing Additional Users to an Index Smart Scale

I've just bought one, tried doing the set up and having the same problem.... cannot see any answers here although seems many people have the same problem Using an iPhone if that makes any difference... ?? Thanks.

2 yrs later I was never able to use it. If I were u, I would return it. I got fed up with it. The iPhone didn’t help in my case. 

I have always had my S2 pair with the WiFi router connected with my ISP.  I have never tried to get a phone of any sort to provide the WiFi used by the S2, and I am almost positive my phone is not involved in the network communication between the S2 and GC. When I had my problem, S2 resets ultimately solved the problem, but as I recall, the problem didn't go away on the first attempt. Try a few more times, finding some independent way of determining that the connection between your router and the internet is healthy at the time.  Good luck!

Same problem here. I'll be contacting Garmin support to ask for help with this.

Edit: somehow it started working overnight, with no additional action from me. I can only assume it was a network problem. Hopefully it continues to work.