Obviously, which I’ve done temporarily. Correct if I am wrong removing NEI server-side reduces NEI functionality. This issue needs to be resolved eventually either by the authors of NEI or sponge development team.
Caused by: java.lang.LinkageError: loader constraint violation: when resolving method “org.objectweb.asm.ClassReader.accept(Lorg/objectweb/asm/ClassVisitor;I)V” the class loader (instance of net/minecraft/launchwrapper/LaunchClassLoader) of the current class, net/minecraftforge/fml/common/asm/transformers/BlamingTransformer, and the class loader (instance of sun/misc/Launcher$AppClassLoader) for resolved class, org/objectweb/asm/ClassReader, have different Class objects for the type accept used in the signature
This is a known problem with the Mixin library. It may do this when a coremod is present