Thank you for trying modem mode. If the issue still persists in that mode then it won't be down to the hub itself as that mode reduces it to a simple modem with none of it's router functions.
Having just rechecked your connection I can now see that your downstream power levels are too low so we'll need to get a technician out to adjust this. I'm 100% sure that's the sole cause of the issue but we'll need to get that fixed first. I've just sent you a private message to arrange the best time for a visit.
It appears that this issues are caused by a faulty SuperHub and this issue only started when I got my speed boost. (Appears to run on a different frequency and fried the Hub).
Virgin need to be more careful as no doubt there are many others in this exact same situation.
Took me ages to get through to someone who wasn't just a scripted no hoper with no idea about network troubleshooting.
I would suggest badgering them on here until someone pays attention as they have done for myself!
Hope you get it sorted out buddy and I would also look at port forwarding to ensure a stable connection and once done it rules out an issue on your side making it more difficult for them to argue with their nonsense!