I've created a throwable sword that spawns itself as ItemStack on impact.
It crashes the game on creating the ItemStack if I uncomment this line:
EntityRegistry.registerModEntity(EntityThrownSword.class, "swordEntity", Config.getEntityID(), MainClass.instance, 128, 30, true);
However if I comment it out the entity logic works fine, but the entity is invisible during flight.
EDIT: The entity was just outside the tracking range, added a acheck to remove the entity before this could ahppen again
Just a tip, the entity IDs won't conflict because it's registering the ID with your modid. So no need to use the configure code.