Sort BuddyPress members by PMPro membership level.

my_sort_bp_members_list.php

/**
 * Sort BuddyPress members by PMPro membership level.
 * Add this code as a code snippet or in a custom plugin.
 * https://www.paidmembershipspro.com/how-to-add-code-to-wordpress/
 */
function my_sort_bp_members_list( $query ) {	
	global $wpdb;
	$query->uid_clauses['select'] .= " LEFT JOIN $wpdb->pmpro_memberships_users mu ON u.user_id = mu.user_id AND mu.status = 'active'  ";
	$query->uid_clauses['orderby'] = str_replace( 'ORDER BY', 'ORDER BY mu.membership_id DESC, ', $query->uid_clauses['orderby'] );
}
add_action( 'bp_pre_user_query', 'my_sort_bp_members_list', 20 );