After being on for a while and the shutter forced open if I force it close, the image is less even but not terrible:
Which LUT are you using? Is it possible in Seek Thermal app disable any LUTs and get grey output?
Thanks to @marshallh he provided another ones raw sensor USB captured images
Played a while ago with those images-disabled any gamma corections in my software and set smooth to level 9 so more averaging, than applied
iron256 LUT mentioned before (2nd row coloured ones)
After that I've converted them to gray again and normalized and... I do not know those images from left to right looks more uniform when we blur them a little bit (average a few times) and normalize or equalize, even using any purpose image software like Gimp starting with this raw sensor images provided by @marshallh
I've included them in last row, with left to right timeing like other above starting from oryginal in the first row...
I do not resized them from its oryginal 208x156 to do not create additional artificial pixels eg. by linear resize 4x to Seek Thermal output resolution 832x624, so they were processed at its oryginal sensor size 208x156.
It is interesting what explanation might be and if it is hardware issue
BTW: Still those last two columns in raw sensor data are mistery-simply skipped them in my image processing and shifted whole image by 1 pixel to nice horizontal fit into 208x156 sensor raw data image size.