I tried logging into https://accounts.google.com/Login
from my S3 as I had the same issue....it worked! Started tidying up contacts that had merged due to JB and cleaned up almost all when the sync stopped again. Login to above account and sign-out and log back in to no avail. Contact Sync stuffed again.
Interestingly enough, SMTP setting dropped out as well. Had to drop that back to no authentication/login but it works.
Anyone comes up with any other suggestions it would be great!