Slash login (/login) leads to 404

Any recent changes in your permalink structure? I’ve encountered that issue in the past when permalinks were set to the default (plain), setting. The redirect from yoursite.com/login or yoursite.com/admin to /wp-login.php will return a 404 error.

I had no changes to the permalink structure.

mydomain/login returns HTTP Response Header Status: HTTP/1.1 404 Not Found. I.e., it does not redirect to wp-login.php.

My other (test) site’s mytestdomain/login returns HTTP Response Header Status: HTTP/1.1 302 Moved Temporarily to Location: https://mytestdomain/wordpress/wp-login.php — even when I deactivate all plugins on that test site. There are no traces of this redirect in the test site’s .htaccess either.

What mechanism is responsible for redirecting mytestdomain/login to https://mytestdomain/wordpress/wp-login.php?

Found the culprit: the plugin “WP Cerber Security” disables the WP core functionality of redirecting a variety of shorthand URLs to the admin (as defined in the function wp_redirect_admin_locations() in the file canonical.php).