First of all, judging by the practice file, you really know what you are doing when it comes to shooting. Obviously, it's partially due to the nature of the rested exercise, but still the fundamentals are looking very sharp.
A solid and consistent approach throughout the entire session
Thus, upon looking through the session, I can't pinpoint any glaring mistake you are making in regards to how you operate the rifle.
However, I think you could experiment with your shooting gear and improve the hold stability this way. The peaks on the Speed Graph clearly correlate with a heartrate (of around 95-97 BPM). These fluctuations are (most likely) caused by how
your heartrate is amplified by either a pretty stiff jacket or undergarment that is not thick enough to buffer the effects of your hearbeat
On top of that, your grip might be too tight judging by the comment you've left on the practice file. The less relaxed you are, the more your heartrate affects your hold stability and the more your (allegedly) stiff jacket amplifies this effect.
I'd recommend looking into different undergarment materials or maybe switching to a less stiff jacket.
Well, that's the best insight I got. Perhaps, some real experts like
@CharlesD could chime in and drop some knowledge