The loopback request failed in Troubleshooting Mode

I host my site on a hostmonster VPS and that means I have complete control over it. The host does not by default prevent loopback requests, so I’ told. WordPress is installed in a sub-directory.

I got this plugin because I was trying to figure out why a new plugin I wanted would not activate.

So, if loopback requests fail even in Troubleshooting Mode I guess that means the request is getting blocked in .htaccess. (That’s really a question.) On that theory I’ve looked at my .htaccess file in the web root and I see nothing suspicious there.

I also checked the .htaccess file in the WP root sub-directory and that has just one entry with 127.0.0.1 printed in it:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_METHOD} POST
RewriteCond %{REQUEST_URI} ^(.*)?wp-comments-post\.php(.*)$
RewriteCond %{HTTP_REFERER} !^http(s)?://<myside>\.com [NC,OR]
RewriteCond %{HTTP_USER_AGENT} ^$
RewriteRule .* https://127.0.0.1 [L]
</IfModule>

I’m wondering if I’m not casting a wide enough net inspecting that .htaccess file. How does the Health Check & Troubleshooting test the loopback request? For example, does it call ‘localhost’ or ‘::1’?

I haven’t ever had problems with my site until I tried to install the new plugin. It’s not a public blog. But now that this plugin is drawing my attention to the issue I’d like to clean it up. Thanks!