Basically, you need to make sure that you’re creating your post types after acf has initialized. You can do this by adding your action that creates the post types with a sufficiently high priority.
add_action('init', 'my_register_post_types', 20); // priority 20 is after acf/init
function my_register_post_types() {
// register your post types
// get_field() should work
}