Hello,

it's a feature to set custom contents of the 404 page not to override it.

It depends on the template used, too.

So to be efective check that your template file error.php includes the call to the getMessage function as the default Protostar: $this->error->getMessage()

About plugins, the System - JSitemap utilities plugin must be enabled and if the Joomla System - Redirect plugin is published it must be ordered before the System - JSitemap utilities. As an alternative you can choose '404 page override mode' -> 'No'

- John