maintainn-cmb-2.php

<?php

/**
 * Handle Team shortcode.
 *
 * @param  array $attr Array of shortcode attributes.
 * @return string $output HTML
 */
function maintainn_team_shortcode( $attr = array() ) {
	// Get post object.
	$post = get_post();

	// Get team members attached to this page.
	$members = get_post_meta( $post->ID, '_maintainn_team_meta', true );

	$output = '';

	// Return empty string, if we don't have members.
	if ( empty( $members ) ) {
		return $output;
	}

	// We have team members and now we can output them.
	$output .= '<ul class="maintainn-team">';

	foreach ( $members as $member ) {
		$output .= '<li class="member">';

		$output .= '<img src="' . esc_attr( $member['photo'] ) . '" alt="' . esc_attr( $member['fullname'] ) . '" />';
		$output .= '<h3 class="fullname">' . esc_attr( $member['fullname'] ) . '</h3>';
		$output .= '<p class="position">' . esc_attr( $member['position'] ) . '</p>';

		$output .= '</li>';
	}

	$output .= '</ul>';

	return $output;
}
add_shortcode( 'maintainn_team', 'maintainn_team_shortcode' );

Excuse me if I comment this code, but I'm a bit perplexed.
I create a group field (here) that it seems similar to your group and so I used your code with my fields in order to create a shortcode (here) but it don't works, and I don't understand why the shortcode didn't print the field values!?
Any suggestions, please?