You’re add_action and remove filter need to have the same priority.
add_action('acf/save_post', 'my_post_title_updater', 1);
remove_filter('acf/save_post', 'my_post_title_updater', 1);
When you run the acf/save_post action with a priority of 1 you will need to use the $_POST['acf'] array to get the values of the other fields.
