I believe that the Velop Mesh system sets up its own range of IP addresses (both for WiFi and for the ethernet ports used for equipment in the units) in your home network, and these are separate from those used by default by your Virgin Hub router.
It may be that your NUC got locked on to the network address range of the Virgin hub.
I would have thought that moving the NUC back to the Velop, and then rebooting the NUC would have sorted things out. Has it not done so?