Sub domain not loading on a different server

Question

I have a domain on one server (windows). This server is handling the DNS. I have a A record for a sub domain on a different server (ubuntu, apahce2). However, when I try to pull this page up it times out. I cannot find anything in the apache2 logs which explains it. When I ping the name for the sub domain the ip comes back correctly. Also, at one point I had the main domain and sub domain all pointing to the ubuntu server and the page loaded correctly. Below is my virutal host file.

<VirtualHost *:80>
        ServerAdmin webmaster@localhost
        ServerName www.sub.domain.com
        ServerAlias sub.domain.com
        DocumentRoot /var/www/html/sub.domain.com
        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined
RewriteEngine on
RewriteCond %{SERVER_NAME} =sub.domain.com [OR]
RewriteCond %{SERVER_NAME} =www.sub.domain.com
RewriteRule ^ https://%{SERVER_NAME}%{REQUEST_URI} [END,NE,R=permanent]
</VirtualHost>