Expected Behavior:
Enderman spawners spawn Enderman at normal rates.

Enderman spawners appear to be spawning Enderman so fast it lags the game after a few seconds.

Other mods (Forge):
Optifine HD_U_G1_pre26
Phosphor 0.5.2+build.4
MixinBootstrap 1.0.3

Mod Version:
0.5.7 for 1.15.2

I will try to fix it soon

Fixed. Update will be released soon