Hub 5 DMZ does not work

I recently had my hub 3 replaced with a hub 5, as I was having latency issues (see this post), and I've tried to replicate my configuration from my hub 3, but the DMZ function is not working. I previously had it set to my server, and I've done the same now, but it doesn't work - all incoming connections are refused.
I know this is the hub's fault and that dmz specifically isnt working, as I can still manually port forward individual ports, like 80, 443 etc to my server and that works - just not practical if I want to have everything going to it.