I don’t know why some customers want to enable all login plugins at once. Those actually don’t increase your security instead just bother you (and your users).
I think the problem is Login Ninja, disable it and try again.
If it doesn’t help this means one of those plugins uses a non-standard way for login address. Plugins should not use ‘wp-login.php’ directly in their source code they should use wp_login_url() function.
HMWP doesn’t do so much in wp-login page. It only need wp_login_url and nothing more so you may need to manually change their source code.