Apache error logs are filled with the logs below.
Quote[error] an unknown filter was not added: DEFLATE
This error message would mean that someone is using mod_deflate code in an .htaccess file, but your server doesn't have mod_deflate installed. Find for the .htaccess file which has the entry for Deflate being used.
If you want to install mod_deflate, simply compile PHP/Apache using
WHM >> EasyApache (Apache Update) or
/scripts/easyapache. Select the Deflate module in the Apache's Exhaustive Options List.