Looks like I was too fast in assuming that Debian suffered the same issue as observed on Ubuntu.
Tests seem to pass at https://ci.debian.net/packages/l/lloconv/unstable/amd64/, no output observed on stderr. Except for one test run on 2018-08-24 03:42:33 UTC (https://ci.debian.net/data/autopkgtest/unstable/amd64/l/lloconv/872144/log.gz). I wonder what changed between that test run and the next one that passed. Not the version of libreoffice in any case.
