I’m wondering if it may be the following htaccess code that WP Rocket adds causing the conflict with SG Optimizer:
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{HTTPS} on
RewriteRule .* – [E=WPR_SSL:-https]
RewriteCond %{SERVER_PORT} ^443$
RewriteRule .* – [E=WPR_SSL:-https]
RewriteCond %{HTTP:Accept-Encoding} gzip
RewriteRule .* – [E=WPR_ENC:_gzip]
RewriteCond %{REQUEST_METHOD} GET
RewriteCond %{QUERY_STRING} =””
RewriteCond %{HTTP:Cookie} !(wordpress_logged_in_|wp-postpass_|wptouch_switch_toggle|comment_author_|comment_author_email_) [NC]
RewriteCond %{REQUEST_URI} !^(.*/feed/?)$ [NC]
RewriteCond %{HTTP_USER_AGENT} !^(facebookexternalhit).* [NC]
RewriteCond “%{DOCUMENT_ROOT}/wp/wp-content/cache/wp-rocket/%{HTTP_HOST}%{REQUEST_URI}/index%{ENV:WPR_SSL}.html%{ENV:WPR_ENC}” -f
RewriteRule .* “/wp/wp-content/cache/wp-rocket/%{HTTP_HOST}%{REQUEST_URI}/index%{ENV:WPR_SSL}.html%{ENV:WPR_ENC}” [L]
</IfModule>
Perhaps that initial HTTP_USER_AGENT check is causing SG Optimizer to think it can’t cache?