Migration went fine apart from the migration to Postgresql 11. I faced the same issue as here Problème de migration postgresql_9p6_to_11.py and installed postgresql 11 manually as suggested there. It did not work unfortunately, here is the log https://paste.yunohost.org/raw/ojoxikejur
Edit: Running Diagnosis revealed that postgresql was not running. I restarted it, which worked! Then I re-run the migration and it worked as well!