Allow large JOIN operations in the Member Directory and Profiles Add On for Paid Memberships Pro.

pmpromd_set_db_option.php

<?php
/*
 * Allow large JOIN operations in the Member Directory and Profiles Add On for Paid Memberships Pro.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 *
 */
function pmpromd_set_db_option() {
  global $wpdb;
  $wpdb->query( "SET SESSION SQL_BIG_SELECTS=1" );
}
add_action( 'init', 'pmpromd_set_db_option', 5 );