Patch to test if BuddyPress Core ticket #6197 contains the right fix (Should only be used with version 2.2.0 when signups are not allowed)

bp-custom.php

<?php
/**
 * BP Custom file
 * see https://codex.buddypress.org/themes/bp-custom-php/ for explanations about how to use it
 */ 
// Exit if accessed directly
if ( !defined( 'ABSPATH' ) ) exit;

function test_retain_register_activate_signup_not_allowed( $page_ids = array() ) {
	if ( ! version_compare( buddypress()->version, '2.2', '=' ) ) {
		return $page_ids;
	}

	$all_page_ids = bp_get_option( 'bp-pages' );

	if ( ! isset( $page_ids['register'] ) && ! empty( $all_page_ids['register'] ) ) {
		$page_ids['register'] = $all_page_ids['register'];
	}

	if ( ! isset( $page_ids['activate'] ) && ! empty( $all_page_ids['activate'] ) ) {
		$page_ids['activate'] = $all_page_ids['activate'];
	}

	return $page_ids;
}
add_filter( 'bp_core_get_directory_page_ids', 'test_retain_register_activate_signup_not_allowed', 10, 1 );