If your problem seems related to debconf database corruption, be it of
above kind or not, the suggested fix is, quoting Joey Hess message in
#198297 bug page

By purging and reinstalling the package, you only fixed the entries for
that package. I suggest you run /usr/share/debconf/fix_db.pl as root,
which will delete all the orphaned questions. You may end up having to
repeat your answers to some debconf questions during future upgrades,
but that's a small price to pay for a consistent debconf database.

After running /usr/share/debconf/fix_db.pl as root, please look which
templates were affected,

$ diff -u /var/cache/debconf/config.dat{-old,} | grep ^[+-]Name
$ diff -u /var/cache/debconf/templates.dat{-old,} | grep ^[+-]Name

Your debconf database should be now in a consistent state and packages
configuration should succeed.