Some server software includes a "mini firewall". Server configuration requires specification of which interface(s) the server will access requests from and/or which IP addresses the server will accept requests from.
Perhaps the server is rejecting the requests you have logged because the server is not configured to accept those requests. There might be a server log giving more details.
That tip resolved it. I was under the impression that I had the "mini" firewall on the webserver disabled for my tests - but I must have been wrong. "Problem" went away when I uninstalled the local/mini firewall that is no longer necessary. We were using an application that sits on top of iptables - and I assumed incorrectly that shutting down iptables would disable the local firewall application. This local/mini firewall must have additional filtering outside of iptables as well.
Now - I have a separate question - how to setup load balancer to work across https connections. Will look around for info, and if needed post it separately.