In my case the subdirectory was "forum", as I run a Kunena forum. I was trying to get the SEF URLs working with Kunena, and I mistakenly added the entry. Now it won't go away.
This is also happening with "affiliate" which I added as a test, again mistakenly.
Somehow, .htaccess Maker still remembers those lines added, and keeps putting them in, even though they have been removed in the backend UI.
Here is the relevant text from the generated .htaccess file:
##### Advanced server protection rules exceptions -- BEGIN
RewriteRule ^administrator\/components\/com_akeeba\/restore\.php$ - [L]
RewriteRule ^administrator\/components\/com_admintools\/restore\.php$ - [L]
RewriteRule ^administrator\/components\/com_joomlaupdate\/restore\.php$ - [L]
RewriteRule ^affiliate/ - [L]
RewriteRule ^forum/ - [L]
##### Advanced server protection rules exceptions -- END
Attached is a screenshot of the UI section, where you can see the lines are not there.
Thanks.