I found that Output.php compresses the output in gzip. This sometimes caused blank pages to appear on the local server.
I have used the Nginx webserver that compresses the pages in gzip itself. I think it does it better than it does at php level, because static content it compresses too.

In ipboard 3 there was an option to disable php gzip.
The option can be added to advanced settings or constants.php. So far I have to edit the Output.php

Why does it cause blank pages, and only sometimes? Do you have any server error logs showing what the problem is by chance?

I think this is a useful feature like BigPipe of Drupal

 

Read also:

https://www.drupal.org/docs/8/core/modules/bigpipe/overview

https://www.facebook.com/notes/facebook-engineering/bigpipe-pipelining-web-pages-for-high-performance/389414033919

This is a good feature to add into system, I hope IPS do it into future.