Hmmm, I believe I have found my problem.
I have configured my router to give the control box a static ip address by binding it to the MAC address.
What I'm seeing however, is that the MAC address has changed.
The last 6 characters are the same, but the first 6 changes.
Can anyone confirm this?
Example: yy-yy-yy-xx-xx-xx changes to zz-zz-zz-xx-xx-xx
So in the end it turns out the control box has requested a DHCP IP and received another than the one I thought I had configured.