After wasting literally hours trying to update maps, the solution which works is to hotspot your phone and have the Wahoo device connect to this.
It looks like Wahoo have a peculiar and very particular sensitivity to public wifi - including services in hotels which are password protected. I cant explain it, but after over 3 hours wasted on different wifi networks, my phone hotspot worked instantly for all maps.
Such shit tech. But hope this helps someone else