I had a 321 member category that wouldn't display all of its members. I am running Mediawiki 1.25.1. I finally got it to work by adding a large enough value for $wgCategoryPagingLimit (default value is 200) into LocalSettings.php.
require_once( "$IP/extensions/CategoryTree/CategoryTree.php" ); $wgUseAjax = true; $wgCategoryTreeMaxChildren = 400; $wgCategoryPagingLimit = 400;