Trying to use the 2x2 player inventory crafting grid causes Minecraft to crash with an IllegalClassLoadError:

org.spongepowered.asm.mixin.transformer.throwables.IllegalClassLoadError: Illegal classload request for accessor mixin tfar.fastbenchminusreplacement.mixin.PlayerContainerAccessor. The mixin is missing from fastbenchminusreplacement.mixins.json which owns package tfar.fastbenchminusreplacement.mixin.* and the mixin has not been applied.

Full log file here.

Same issue on a fresh instance with only forge, mixinbootstrap, and fastbench.

hmm, try redownloading, it seems like the jar might've corrupted