A small update: After checking the back-upped database structure (searching for
'ovirt_engine_history' inside the 'engine' database), we found that the
ovirt_engine_history user was also having permissions to a table in the engine database,
probably causing the user to be created before the restoration of the history database
took place. After removing the user permissions in the active environment (4.3) we were
able to bypass this problem.