sometimes if you name the material assigned to a face any color thats already in the blockland assets (like red, yellow, blue, ect.) if blockland cant find that material in the add-on, it will replace it with the default material with the corresponding name in the actual game files.
a list of these colors are found in base/data/shapes
so what i would do is open that hat in blender and figure out which material it is that doesnt have an actual texture for it.