Superhub : Superhub 3 Intermittent problems over Christmas

[DamnMachine]

I had some strange broadband problems over Christmas and New Year and would value any opinions from the community.

The short version of this is that my Superhub3 was extremely unreliable, failing once or twice per day, from Christmas Eve to about New Year's Day.
I spent many hours on the phone with Virgin, and finally got them to book an engineer to come out next Saturday.
However, since New Year's Day it seems to have worked perfectly, no problem at all.
So the nub of the question is whether it is worth staying in for the Virgin engineer, or shall I just cancel him.

A bit more detail:

May or may not be relevant, but about mid November the Virgin Superhub2 which had been working fine since January completely failed.
Virgin support could not get it to come back on-line, so they sent me a new Virgin Superhub3, which worked perfectly for about three weeks.

Around about Dec 23rd, we lost connection to the internet. I restarted the router and it came back, but this happened again once or twice a day over the Christmas period. Sometimes a re-start would bring it back on-line, sometimes it would take several restarts and Virgin support to send some kind of signal to it, and in at least one case I could only bring it up again by factory resetting it.

When I started investigating the failures, some strange things emerged.

Firstly, once it had failed, I couldn't access it at all via the web management interface. So it seemed like it wasn't the outbound link to the internet that had failed, it was the whole hub.

Secondly, I had several cases where one of my devices would connect to the internet just fine, while another could not connect to anything, not even pinging another device on the same hub by IP address. In these cases it was often one of the wired devices that wouldn't work, but not always the same device or the same port. In some cases I was able to bring it back just by disconnecting the Cat5 cable and plugging it back in again.
I also replaced one of the cables to see if that was the problem, and it started to work again, but then had another failure.

I have a fairly complex set up: wifi off the Superhub, three wired devices off the main hub, the fourth port connected to a switch which connects another three devices, and also a Powerline network which reaches another wifi router acting as a slave to the Superhub. So one possibility is that one of those devices was playing up. My next step was going to be to replace the switch, but I haven't done that since I haven't had a failure since New Year's Day (and I don't want to disturb a stable system at the moment).

My current working theory is that something was happening which was somehow disabling the entire hub, including causing some of it's Ethernet wired ports to stop working even when the wifi was still working ok.
But since it's been working fine for nearly a week now, I'm wondering if there is even any point in having an engineer out.

It will depend on who you get, but if it's a bad one he will be in the house for two minutes, say "all looks ok to me" and bugger off.

Surrey/Hants area.

Any thoughts or advice?