It appears as though when looking for texture variants, ETF does a resource manager lookup every frame for every entity to find whether there are available variants.
This essentially means that ETF is reducing game performance based on the speed of your hard drive or SSD.

A better method would be to resolve available textures during resource reload, and cache those to be checked later during rendering.

Spark profile: https://spark.lucko.me/z9b0Ohaf0A
Image of relevant performance hit:

hmm it should only be doing that check once, it's definetly not meant to every frame, i'll look into it

for the meantime version 3.1.2 should not have this issue, someone else has reported this seem to be only the recent sheep wool support addition

it was a much larger issue, an easy fix though, I am quite surprised it escaped notice for so long, i'll have a fix up tonight

this has been fixed and will be in release 3.1.4 later tonight I will keep the issue open for awareness until then

the fix is up on curseforge and modrinth

thank you for showing me spark btw, this will be very handy