Regarding ‘hot spots’ ……
These can be caused by nothing more serious than a spec of debris getting onto the microbolometer window. The dirt or debris that is on the window reflects the microbolometer die temperature back at it, causing the hot spot. A careful clean of the microbolometer window (not the lens) will often remove the issue.Before anyone asks, I cannot provide a guide to cleaning their particular microbolometer, except to say you need good access to the window by either removing the lens or the microbolometer from the core chassis.
As to where the first or debris comes from…… budget manufacturing facilities with less than perfect microbolometer core hygiene. Foreign bodies within the core capsule can move around and drop onto the microbolometer window. A photographic air puffer through the lens mounting hole can sometimes clear the problem. You need to reset the lens focus point after removing it.
Fraser