Change of Multisite Domain - enable Cloudflare on Siteground
After Cloudflare was enabled on Siteground, The Network Admin was end up with a redirection loop, while the primary site was functioning in anyway.
Issue
A surge of connection to the shared server has caused Siteground to restrict access to the site hosted. As they suspect it was a DOS attack (Denial of Service attack) or the Slashdot effect. Cloudflare was required to enable in order to lift the restriction.
However, after Cloudflare was enabled and Siteground have lift the restriction, The Network Admin was end up in a redirection loop, while the primary site was functioning in anyway.
Domain Change
The issue was caused by the domain change to use sub-domain www to replace the existing domain. While WordPress Multisite has been in additional Database tables and fields that requires to be update during the process, siteground did not handle it properly.
Solution
Follow the standard procedure of domain change on Multisite WordPress to identify which domain update was missing.
In this case
wp-config.php
define('DOMAIN_CURRENT_SITE', '<newdomain>');
wp_blogs
domain: newdomain
wp_options
siteurl: https://newdomain
wp_site
domain: newdomain
wp_sitemate
siteurl: https://newdomain
Checklist of Changing Domain
Redirect from origin to the new domain
.htaccess
RewriteEngine On
RewriteCond %{HTTP_HOST} ^origin.com [NC]
RewriteRule ^(.*)$ https://newdomain/$1 [L,R=301]
Change URL on Database
Search and Replace
replace all instance of origin domain with the new domain