Package: syslog-ng Version: 3.28.1-2+b1 Link /etc/systemd/system/syslog.service still points to /lib/systemd/system/rsyslog.service which does not exist after installation syslog-ng. The link should be processed in the "install" section of /var/lib/dpkg/info/syslog-ng-core.preinst script too. Maybe it is the rsyslog package which should take care of.
Peter