CSCO11593588
I know it's a while since you asked the question, but I recently faced the same issue and thought I would leave a comment in case you or anybody else still have the issue.
I found that the IOS XRv virtualbox image needed to have valid NIC settings configured on boot, in order to add the physical interfaces. It wasn't enough to enable the NIC's they also had to have a valid setup. I used a hostonlynetwork (ensure you have one setup in virtualbox file/preferences/networks/host only networks). After the 1st boot with the interfaces configured in this way GNS seems to take over the config of the interfaces, and during operation they show the UDP ports related to each interface in Virtualbox, and when the image is stopped all the NICs show as disabled. But once they are created they re-appear on each boot.
Oddly I found
e0 - G0/0/0/2
e1 = Mgmt
e2 = G0/0/0/0
e3 = G0/0/0/1
Which is an odd relationship that I do not understand.
Regards
Martin