Whenever you are using [Nginx + Varnish + Apache] or [Nginx + Apache] you need to tell Apache that a SSL request is being served by a proxy server. So use the code below to force SSL .htaccess
SetEnvIf X-Forwarded-Proto "https" HTTPS=on
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteCond %{HTTPS} !=on
RewriteCond %{HTTP:X-Forwarded-Proto} !https [NC]
RewriteRule ^ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]
</IFModule>