It would help to see if PHP reports an error. There server for the wiki returned this to me;
Server: Apache/2.4.6 (CentOS) OpenSSL/1.0.2k-fips PHP/5.4.16.
I'm a Debian guy, so I googled for the PHP error log location for CentOS and it seems to be;
/var/log/php-fpm/www-error.log
|