The error comes from the app itself, so the safest way would be to get in contact with OpenProject, but this may be because of your UCS PostgreSQL installation. You should try to upgrade it if you are still running (now unsupported) version 9.6: Updating from PostgreSQL 9.6 or 9.4 to PostgreSQL 11
Your app setup works until these warnings are omitted, as I don’t know the app I cannot tell you if these are critical. @Alex-Ander s output contains a datestamped schema version, but yours is 0, that sounds suspicious.
Maybe someone else has any idea, I sadly cannot reproduce it and have no further app knowledge.