Please redownload Sync from the following urls & reinstall. Fixed.
http://sync-jenkins-artifacts.s3.amazonaws.com/sync-nas/2.6.3/Debian/resilio-sync_2.6.3-1_amd64.deb
http://sync-jenkins-artifacts.s3.amazonaws.com/sync-nas/2.6.3/Debian/resilio-sync_2.6.3-1_i386.deb