I had many issues by upgrading my Wazo from 18.03 to 19.16 and how I made it:
Moving files issued by previous upgrade
mv /var/lib/xivo-upgrade/xivo_user_dump.json /root/
mv /var/lib/xivo-upgrade/xivo_service_dump.json /root/
Undefined LANG locale (I was as FR, inherited from my terminal) as scripts are making check on “Installed” package (my system return “Installé”).
And finally run the upgrade