“…No PHP or .htaccess files themselves are actually ever cached. So say the cache on your website testwebsite.com has just been cleared and I request it from IP 1.1.1.1. Because no cache exists on the server for that domain, it’s going to ask for a copy from the backend server and show that IP 1.1.1.1 is requesting it. Now, if my IP (1.1.1.1) is set to say a deny all directive in .htaccess, because it reaches the backend (due to no cache existing) it’s going to refuse to serve me the page….”
Well what you can try that might logically work is to whitelist the additional IP addresses like the same scenario that would be needed in an X forwarded for type of scenario. You will need to get those IP addresses from your Host since they are internal and not displayed when I check DNS for this website.
You would add those additional IP addresses using the Plugin Firewall >>> Additional Whitelist Tools >>> “Allow from” Whitelist rules tool.