Restoring config files from debs is not straightforward. We won't now
know what removed it, but, for example, if a mistake happened and for
some reason "rm -f /etc/ipsec.conf" was run, special flags have to be
given to dpkg to restore a missing config.
Since you restored it already, there is
If installing the package doesn't restore ipsec.conf, then it's because
it was removed outside the package's control, usually.
Could you check /var/log/apt/history.log to backtrack the packages you
installed and upgrade to see if there is a clear way to reproduce this
problem?
That being said,
