So even with a new hub 5 I was still getting the same intermittent connection issues and MDD timeouts in the logs.
Got the engineer out again to try a Hub 4 instead. It's been a couple of days and not had a single disconnection and no packet loss on the BQM. Latency is a bit all over but that's not really an issue that I can see when I'm using my devices.
Based on that there are definitive issues with the Hub 5, probably firmware related. I'd advise anyone getting a hub 5 not too and ask for a hub 4 instead at least for the next 6-12 months, not worth the hassle.
Anyone experiencing MDD timeouts and other intermittent connection issues - if you recently got a hub 5 and have only started experiencing this since the hub 5 was installed, then I'd recommend replacing the hub 5 with a hub 4.