Thanks for the input. It seems like that, indeed.
It is the original X360 Kinect camera.
The proper installation of the camera (i.e. camera lens & IR being unobstructed) has been checked numerous times now, quite elaborately so, even, yet still the issue persists.
Changing the main height value in the BoxLayout also does not improve things, and even makes the application freeze or crash.
Other than in the affected (green) area, the system does function properly, i.e. it projects well and updates the projection based on physical changes made in the sand below.
Nevertheless, this is quite an unsustainable situation, not only because the system now fails to represent the AR Sandbox (software) in its full glory, but especially because it is currently right in the middle of being rolled out into production in an educational environment.
Could it be anything in the application, itself? And is there any other way we could troubleshoot & doublecheck any issues that might somehow be lingering on the hardware-side, after all?