I get this error in the Apache error log when I enable any optimize options.
"Require not allowed here"
The optimization doesn't happen, and the CSS is not applied.
Trying to view any of the generated CSS files causes the same error, eg:
/content/cache/autoptimize/css/autoptimize_d123098829b02f0080de0482f3048288.css
https://wordpress.org/plugins/autoptimize/
If I comment out the line "Require all denied" the CSS loads ok.
If it makes any difference, I use Capistrano to deploy the site, and the content/cache directory is symlinked.