get_fields not returning all fields

I have a custom post type with about a dozen custom fields. Before rendering the template that displays this post type I create a new object with this constructor:

/**
	 * Initialize the class and set its properties.
	 *
	 * @param WP_Post|null $post
	 * @param array        $meta
	 * @param array        $fields
	 */
	public function __construct( ?WP_Post $post, array $meta, array $fields ) {
		$this->post   = $post;
		$this->meta   = $meta;
		$this->fields = $fields;
	}

I initialize the last arg with $fields = get_fields( $post_id ). When I run this in Xdebug, however, that $fields arg only contains a limited set of the total fields for that object. I have to instead run get_post_meta and work with the raw meta values instead.

Start with the reported get_fields($post_id) call and compare its returned fields with the values from get_post_meta. Confirm which custom fields are omitted and under what post conditions; done means get_fields returns the complete set of fields expected for the custom post type.