I bought my Galaxy s7 Edge just about two weeks ago and just yesterday I started experiencing the dreaded #At&T Address book sync" I noticed that it began to drain the bejeebies from my battery, 30% in and hour. I was able to disable it for now by the descriptions from previous authors.. Once it appeared on my pop up I long press, it takes to the app, then I tap the FORCE STOP, I then clear Cache, clear Data, then i go to Permissions and I disable all option (Contacts, SMS, etc ) then I reboot, the PopUp will come back saying !Address book sync has no permission! it will clear after a few minute and it will no longer appear... That was my solution... I hope this helps