private static function get_group_slug( $group_id ) {
		global $acf_local;

		if ( isset( $acf_local->groups[ $group_id ] ) ) {
			// First try the local groups (added by PHP).
			$title = $acf_local->groups[ $group_id ]['title'];

		} else {
			$title = '';
			if ( is_numeric( $group_id ) ) {
				$args = [
					'post_type' => 'acf-field-group',
					'no_found_rows' => true,
					'update_post_meta_cache' => false,
					'update_post_term_cache' => false,
					'fields' => 'ids',
					'post__in' => [ $group_id ],
				];
				$groups = new \WP_Query( $args );
				$acf_groups = is_array( $groups->posts ) ? $groups->posts : [];
				$acf_id = empty( $acf_groups ) ? 0 : $acf_groups[0];
				$title = get_the_title( $acf_id );
			} else {
				$group = acf_get_local_field_group( $group_id );
				$title = empty( $group['title'] ) ? $group['title'] : '';
			}

			// Patch for the new version of ACF Fields plugins >= 5.4.*.
			if ( ! $title ) {
				$groups = acf_get_field_group( $group_id );
				$title = empty( $groups ) ? false : $groups['title'];
			}
		}

		if ( $title ) {
			return strtolower( str_replace( ' ', '_', $title ) );
		}

		return false;
	}