Disabled Foreign Key
Foreign keys are often disabled when bulk loading data into a table to improve performance. It's easy to forget to re-enable them after the event, meaning the foreign key doesn't get applied for any future updates or inserts.
Re-enable the foreign key, if still needed. Note that re-enabling the foreign key will cause all table rows to be checked for integrity, so this should be considered when scheduling the SQL.
Drop the foreign key if no longer needed.
Any suggestion from Aireforge should be thoroughly tested before being implemented into production.