php "require_once" includes file twice and fails | htaccess mod rewrite active - php

Question

I use require_once in different files.
After applying .htaccess redirect rules it still worked flawlessly on localhost but stopped working on the server.
I deleted a require_once line and then it also worked on the server.
The two directives that do include the file
require_once __DIR__.'/myfile.php';
require_once 'ECCO/CONF/myfile.php';
What could be the issue? Is htaccess redirect a known issue for include?
The .htaccess files are not identical and on localhost there is a directory in the URL
localhost/dir/<redirect part ... >
eg
localhost/dir/EN/page/add/
or
sub.mydomain.com/<redirect part>
eg
sub.mydomain.com/EN/page/add/
The question might be too vaguely phrased and as it works it is low priority. However, a require_once should not conflict IMHO.
htaccess file:
AuthType Basic
AuthName "Password Protected Area"
AuthUserFile ../../htpasswd
Require valid-user
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_URI} !(\.css|\.js|\.png|\.jpg|\.gif|robots\.txt|.ttf|.woff|woff2|.php)$ [NC]
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^[^/].*$ index.php [L,QSA]