404 redirect going to login Page Concrete5

I have an old Concrete5 website I have inherited and a strange issue with our 404 redirect page. I see in /concrete/single_pages & /concrete/views/frontend page_not_found.php files but any 404 redirect goes straight to the login page instead. I don’t see a 404 redirect page in the Sitemap either. How would I get the 404 page working again?

Concrete5 8.5.7

More than likely its due to page permissions on the 404 page?

@TMDesigns much appreciated