Each card needs to be flashed separately from the original image from us, inserted into a raspberry pi and kept on that box. The BoxId is automatically created on first boot up of a new image. It uses the MAC address of the Raspberry in which is inserted.
What's happening to you shows that the image you're flashing already has a boxId set and thus all your boxes are assigned the same id.
Another way to fix this is by running the following commands on each box from the command line:
sudo service astrobox stop
sudo rm /etc/astrobox/box-id
sudo service astrobox start
This should re-generate the boxId and make each box different.