You have a chicken and egg problem going. login_init is called PRIOR to the user actually logged in. It just indicates with the login page has been displayed.
(https://developer.wordpress.org/reference/hooks/login_init/)
The hook should be: wp_login. This fires after a user has successfully logged-in.
https://developer.wordpress.org/reference/hooks/wp_login/
add_action('wp_login', 'redirect_logged_in_users');