Revisiting this issue with the camera core, it resembles what I saw when a cooled cameras fpa became detached from the 'cold finger'. I have to wonder whether the microbolometer die in your core has become in some way detached from the peltier temerature stabiliser on which it is normally mounted. The stabiliser creates the correct working temperature for the die and any loss of the thermal bond between the two will create a thermal gradient across the die. The item that is loose within the microbolometer module could be either the ceramic cement used to mount the peltier elements to the die or even part of the peltier element that was damaged by physical shock. This is all conjecture on my part though and sadly the only easy way to determine the situation inside the module is to open it and carry out an autopsy. Such will destroy the microbolomter module.