Wow... At first glance this looks "electronic" in nature.
(The fact that it is brightest on the left edge and then trails off...)
In the frames that contain this artifact... is it confined to the exact same pixels? probably electronic
If not- is the pattern fixed and it shifts around when you move telescope (dither)? probably very weird scattered light...I have never seen an example of
If not- do other frames show same kind of artifact... though at random rows? probably electonic
I would be curious to know the answer when you have solved it. Electronic stuff, if it is the case, is often an interference, crosstalk, or power supply kind of issue. The TEC for example can be an issue.
-adam