Just an update;
Engineer came this morning, spent a lot of time trying to diagnose. I must say, he was one of the good ones - those you call 'above and beyond'.
I showed him the issue, also proved it on a different laptop. He advised never come across this, and spoke with a few seniors on the phone, who said it sounds like the hub 3 box thinks it's being attacked or being overloaded (even from going on just one website) and for that reason, it's rebooting it.
Eventually, he came up with a suggestion of trying the Hub 4. Once he got authorisation (after some difficulty), swapped it over, and has since been working fine.
I will try this out at a family members house, who recently got VM, to see if that was just my connection and Hub 3, or every Hub 3 has this 'bug'.
Spoke with Nord support, they said issue is to do with ISP modem, and possibly the way it handles traffic.
Edited by JakeRoof (Mon 21-Jun-21 12:41:11)