I thought it was something on the camera but in the very first NVR screen "Local", there's a menu I've not touched before "Live View Parameters". In the "Encryption Key" there were the black dots indicating "something" was configured and I was loathe to touch it as I had no idea what was entered there. Anyway, I did change it to the same authorisation key ("Verification Code") I entered in Hik-Connect for the NVR when setting the initial parameters, and now it all works.
It seems that Hik-Connect and the NVR use an encryption and to see Live View on the NVR through the web browser you also have to enter the key in the field mentioned above.
Incidentally, on my iPad's IVMS-4500, under "Devices" you also need to input this same "Verification Code".
I'm happy as this encryption should stop any hacker from viewing my cameras.