Not 100% sure on the hardware version number

So Im in the UK and have a virgin media superhub2 (which is not great) which I then have connected to a decox55 mesh network.

I have the deco running in wifi router mode and connected to the hub (which is also in router mode).. basically double nat..

It was/is all working fine but then the virgin router goes belly up for a number of days and wont connect to the internet. What I then found was that even though the deco wifi was up I was unable to connect to the dec  hub with the app reliably . It would either time out, or work for a min or two then disconnect.

Any idea why? I would expect the deco network to work fine even if the main internet was down , of course dns etc wouldnt work, but im using ip addresses.

edit :  Alas internet is back up and running and everything running as normal, but any ideas why this was happening?

Any ideas?