Sadly, I think this one is a pixi issue. I tried reproducing the issue with v4.8.9 and it looks fine with and without animated SV battlers on. I have read that later versions of pixi do some weird stuff to MV.
Viewing post in RMMV Rythane Battle Effects Plugin comments
I actually re-tried this with the pre-fix version I still had and it was the same, so yeah I guess that one's out. Sadly, pixi 5 is kind of needed for the performance boost since I'm making a 3d DRPG in MV3D; without it I chug on 20-30 FPS in my 3D dungeon spaces.
But no worries, the other stuff is still worth the price, especially the glowing auras for my enemies in specific states, so thanks for your support and plugin.