The issue might actually be worse than this. I just tested the MZ version of this plugin, and it also seems to have the memory leak. However, there was no need to continually apply and remove the glitch effect. Just turning on the glitch effect once, and letting it stay on, caused my RAM usage to continually increase. I didn't time it super accurately, but as far as I could tell, it seemed like the memory usage ticked up at exactly the same rate that the glitch effect occurred.
So I just want to corroborate that the memory leak happens to me too. I ran two tests - one with the Horror Effects plugin enabled and one with it off, both for 15 minutes.
I ran back and forth around in an empty map (no parallels, only 4 events).
With Olivia's Horror Effects constantly being reapplied to an event via a Show Choice command, the memory usage often climbed significantly. Strangely though, it never got so high it would crash, even for my potato laptop, capping at 900-ish MB. But it would lag horrifically, with the FPS being dropped to 28-ish and the game stuttering as the player moved.
With the Horror Effects plugin disabled, the FPS drop doesn't happen at any point.
As much as I like the Horror Effects, I'd much rather not deal with this.