My old Netgear Nighthawk R7000 works with my Hub 3 and worked my previous Superhub 2 without any issue, just plug and go, but some of the newer Nighthawks seem a bit more temperamental. This thread is similar to your issue:
https://community.virginmedia.com/t5/Networking-and-WiFi/Netgear-Nighthawk-AX8/m-p/4171809
However it shows no clear resolution other than changing some settings on the Nighthawk seemed to fix it.
The cable setup in your picture is weird as only one Ethernet port can be active in modem mode and I have never seen an Ethernet cable taped to the coax cable before.
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Scott
My setup: VM TV box, M350 Fibre broadband with Hub 3 in modem mode connected to a Netgear R7000 router. Telewest/VM user since 2001.
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