EasyQuery::StatementInvalid: PG::GroupingError: ERROR: column "projects.lft" must appear in the GROUP BY clause or be used in an aggregate function...
Postgres databases are more strict then mysql especially when it comes to grouping. This kind of internal server error must be fixed in code.
Try to find out on which page this error appears (url, production.log...), or any other circumstances, that could help the developer to identify the problem.
If possible, always try to upgrade to the most recent version first.