Vulcan, thank you Mate, that's excellent news!, you'll be getting the stutter, but not noticing, I'll check in a sec, but I've been watching the flag or the tower clock, and you can see them stop flapping/ticking as you get the spike
Watch the clock :
I think I know where you're headed with the network card questions, and this machine (where i'm doing most of my testing) has a RealTek Semiconductor RTL8168/8111 PCI-E Gigabit Ethernet NIC, all the "green" ethernet options disabled, in driver as well as power management etc, Gaming machine is using Intel Ethernet Connection I219-V (green settings/power management disabled) and is Intel Core i7-8700, 3080Ti and 32GB ram
Home network is gigabit fibre 1000/400 going through a Ubiquiti UniFi Enterprise Gateway Router (USG-AU).
As you've got such good visibility of your network with the XG, and if I may be so bold, and if you have time, a 30 Min DX9 test would be valuable, and appreciated, it'll be the last testing I'd ask from you, promise!
I did also try some linux utilities to do UDP ping/trace (hping3 for example), but couldn't get a reply, I had the idea that maybe a dynamic table of IP's was being created in the alleged firewall, via a (totally imagined!) process of
Start AH game, and log in, some handshaking is done checking login details are a current subscriber and if so, add the IP to an "allowed IP's table" and let user into game, so I launched the game first and then tried hping3, but still no response to UDP ping, I suspect that as you say Vulcan, it's encapsulated in the game traffic and avoids the bot scans etc etc