I found the extension does not work when a page name contains characters used in regular expressions. I had to modify HierarchyBuilder.php this way:
When there is a string comparison with preg_match_all, I first modify the $currentPagePattern
$currentPagePattern = '/\[\[' . '\Q' . str_replace('/','',$targetPageName) . '\E' . '\]\]/';
and the I do the same for $row in the comparison, example :
preg_match_all( $currentPagePattern, '\Q'.str_replace('/','',$row).'\E', $matches );
This solves my issues with Hierarchy Builder.