MTLLoader: Cannot read property ‘elements’ of undefined

Uncaught TypeError: Cannot read property ‘elements’ of undefined

at Matrix3.copy (three.module.js?0371:3277)
at refreshUniformsCommon (three.module.js?0371:23180)
at setProgram (three.module.js?0371:22963)
at WebGLRenderer.renderBufferDirect (three.module.js?0371:21822)
at renderObject (three.module.js?0371:22575)
at renderObjects (three.module.js?0371:22548)
at WebGLRenderer.render (three.module.js?0371:22312)
at Object3D.draw (Object3D.js?2363:160)`

I have a 3D model (.obj) using three from npm. This is an ES6 project using Webpack.

I am using these dependencies:

import * as THREE from 'three';
import OBJLoader from 'three-obj-loader';
import MTLLoader from 'three-mtl-loader';
import OrbitControls from 'three-orbitcontrols';

The model is resolved and loaded. Texture files are resolved and loaded – the .mtl and the single .png

If I call:

mtlLoader.load(materialUrl, ( materials ) => {
    materials.preload();
			
    objLoader.setMaterials( materials );

The app crashes on the error listed above. On objLoader.setMaterials.

If I comment that out the App works.

Three.js version

• Dev
• r88
• npm latest

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

• [] All of them
• Windows
• macOS
• Linux
• Android
• iOS

Hardware Requirements (graphics card, VR Device, …)

NVIDIA GTX 970 in Sli. Asus motherboard. Output over HDMI 2.0. Doesn’t seem to be related to either hardware, or OS.