This should help. I got it here: https://getwpo.com/faqs/
I see garbage characters instead of a normal web site, how do I fix this ?
If a theme or its files use the call php_flush() or function flush() that will interfere with cache, making the plugin send cached files before essential operations have finished. The flush() call is no longer necessary and should be removed.
Some hosting providers, such as GoDaddy or wordpress.com, provide their own caching solutions. This will often interfere with WP-Optimize’s cache, and could result in those garbage characters.
Using other speed plugins that force GZIP output can result in this issue. One example is the GZIP compression feature in the plugin “Far Future Expiry Header”, or the setting “enable compression” in the plugin PageSpeed Ninja, which are not compatible with WP-Optimize.
To find out if this is the issue, you can search the code for ob_gzhandler or gzencode. If any of those two strings is found (outside of WP-Optimize), it could be the source of the issue.
