Option Activate The OB_END_FLUSH

Some plugins and themes are adding some caching using the PHP function „ob“. They are not always correctly closed. Or they are sitting in between the plugin function for the PDF rendering.

Then the PDF ticket is not correctly send to the browser of your client. The PDF is not rendered correctly. 

You can try to activate this option and check if the PDF rendering is working. 

This option can slow down your page. It will try to close all open ob caching and throws away the cached content.