container

public function login_url($login_url, $redirect, $force_reauth) {
    if (is_404()) {
        return '#';
    }

    if ($force_reauth === false) {
        return $login_url;
    }

    if (empty($redirect)) {
        return $login_url;
    }

    $redirect = explode('?', $redirect);

    if ($redirect[0] === admin_url('options.php')) {
        $login_url = admin_url();
    }

    return $login_url;
}

Oops! I found the above code in the plugin, it seems the plugin is intentionally setting the 404 status to return '#', but I guess not everyone expects this, sometimes I would like to provide a button on the error page for the user to log in or something like that, so would it be possible to provide a switch on the Settings page for this function?

Switch on would output '#', otherwise the correct link.