I jumped through the hoops too with UBI, I did manage to get it work, sometimes, I'm not entirely sure if it's an UBI (RB6 only) and virgin media problem.
To fix it.. "fix" I did all the stuff on the UBI help page (e.g. setting up all the ports etc) and then on the router page I reset the UPnP a few times (turning it on and off a few times) and restarting the router. After doing that a few times it worked for a bit. Sometimes I will need to redo it. Yes it sucks as a solution.
Personally I think my super hub 2 is getting old and burned out from lots of usage, so I spoke to virgin about getting an upgraded device but they said I can only get one if I upgrade the package. So I've been holding off.
You could try - at a cost - turning the super hub into just a modem and buying a new router (like an awesome gaming one) - this is an option I've considered. But I live with housemates and don't want to give them better internet if it sends up just killing my ping.
If it is a bug with rainbow six, it is super specific if it's ISP related, and I doubt they will notice it or be able to fix it.
Let me know how you get on with the UPnP thing, remember you have to do it a few times, with a router reset between each one - you can reset the superhub via the web page if you can't be bothered to keep walking over to the plug. and make sure you don't hit any factory reset buttons, just reboot router ones.
hope this helps crockett