ShirleyWA
iPF Noob
I have had the same thing happening for a while and think we have sorted it out. Found out two days ago that the mysterious gem sender was my brother in law. Sister rang to ask why I did not return them. Turns out he was not using game centre, but all his friends who used DV that where on Facebook where on his list, including me. But seems I could not see him as I was logging into DV through GC.
So he signed into GC and added me and now he is on the list.
Not sure why this is so, but I can at least see him now and return gems.
Si
You may have solved the mystery! I do have Fb friends who play, but their real names show when I sign in through Fb. Will message them and ask if they are the secret sender. Thanks for the idea!