I wasn't really aware that there's multple "Furry Visual Novels" discord servers.. I think the one I joined awhile back is now an "old" one, heh.
It turned out, shortly after posting the above, I realized the problem was alot easier to fix anyway.. Just to post here: In the dust effect file, simply replace every instance of "renpy.random.X" with just "random.X".
Basically, "renpy.random.X" participates in the rollback system, wheras a bare "random.X" does not. The intent with renpy.random is that random generated numbers can be replayed (get the same already generated numbers) in case players roll back or forward during the script. For effects like this, there's obviously no need for that. In the effect, there's an additional slight bug with the way the transform calculates the random numbers that causes the random numbers to be generated far more often than intended (the entire period where alpha is < .01 ), so each particle genreates alot of random numbers. Since renpy.random was being used, this meant that the rollback data stack was growing at a moderate pace while the effect was on screen (eating memory, and also being saved into every save file).