I'm just preparing an update for Leap 42.1 for another bug and along the way I update the package from 3.7.1 to 3.7.3. Please check, if it resolves your problem: https://build.opensuse.org/package/show/home:czanik:branches:openSUSE:Leap:42.1:Update/syslog-ng.openSUSE_Leap_42.1_Update