Here is a very trimmed down version. For obvious reasons I cannot show the actual rack content, but the important part still occurs.
If you notice the red rounded box with several RJ-45 ports inside (besides the KVM port list box), it is currently grouped and shows the problem. If you ungroup it, the problem disappears, and if you re-group again, it comes back.
I'm truely not sure what is causing this (to be fair, I didn't create this file originally, so it could be a carry forward setting of some kind).