With the LAN / Ethernet ports I think there are two issues at play. The first is that the DHCP server is a bit temperamental and suffers from "Not invented here syndrome", so when you come to a replacement scenario, such as moving from one VM Cable Modem to another or from one Broadband supplier to another the DHCP doesn't know what to do with pre-allocated DHCP addresses for which the lease hasn't expired (i.e. ones this new box didn't allocate).
I also don't think the DHCP service knows what to do with pre-allocated IP addresses below its current IP Allocation range (default is 192.168.0.10 - 192.168.0.254), so if you have the VM Super Hub 3 allocated to 192.168.0.1 and other devices with DHCP Reserved IP addresses in the range of 192.168.0.2 - 192.168.0.9, I don't think the Super Hub 3 knows how to handle them.
The second issue is one of the power utilisation across the LAN / Ethernet ports, in that if you suddenly plug in more than one cable you will get a drop out which will only correct itself by unplugging each of the network cables and then reconnecting them slowly one by one.
I wrote a long article on this matter and ways to resolve it earlier today, but it seems to have been deleted or at least sent to moderation. Possibly I have hit upon a touchy subject.
Anyway, that is my view on the problem of which I have long suffered and the workaround I've come up with. Not ideal, but the only real solution is for Virgin Media to fix the problems which they seem glacially slow at doing.
"It's interesting that someone mentioned a faulty LAN cable in a previous post on this thread, which appeared to be working but which was preventing the whole system from functioning. I may have a go at taking all the cables out later and putting them back in one at a time to see if this helps."
You're not hallucinating.
I've had this exact issue this morning with my brand new replacement Super Hub 3 and one of my Cat 5 LAN cables. Not sure in what sense the Super Hub 3 thinks this cable is faulty as it works with other network devices I have, but when I plug it into one of my laptops and then plug the Cat 5 LAN cable into the back of the Super Hub 3, suddenly, *BANG* all of my LAN / Ethernet ports lose connectivity and it only recovers by removing the cables and plugging them in slowly, one by one, except the cable the Super Hub 3 has determined to be "faulty".
As I said previously, the LAN ports seem to be very sensitive about power utilisation or something and if that is overloaded / draws too much power it has some kind of drop out (possibly protective and possibly useful), but since we get no feedback either way its difficult to tell.
You are getting too many problems with the SH3. Just put the wretched SH3 into modem mode and connect it to a decent wireless router.
Somewhat irrelevant now as I have issued Virgin Media with a formal notice of termination of contract. Wasted too much time with equipment that doesn't work for the vast sums that I am paying them each month.