Cube Shader problem

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/stats.js/r16/Stats.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r120/three.min.js"></script>
<script src="https://threejs.org/examples/js/controls/OrbitControls.js"></script>
<script src="https://threejs.org/examples/js/libs/stats.js"></script>

<div id="stats"></div>

CSS

body {
  background-color: #000;
  margin: 0px;
  overflow: hidden;
}

JavaScript

/*
  First test:
  	near line 60 -> comment out both lines applying texture to the objectMaterial
    -> cuberoom shader will stop working
  
  Second test:
  	change threejs reference from r120 to r121
    -> cuberoom shader will not work wheter objectMaterial texture is set or not 
*/

var renderer, scene, camera, controls, container, stats;

init();
animate();

function init() {

  stats = new Stats();
  container = document.getElementById('stats');
  container.appendChild(stats.domElement);
  
  console.log(THREE.REVISION);

  renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(window.innerWidth, window.innerHeight);
  document.body.appendChild(renderer.domElement);

  scene = new THREE.Scene();

  camera = new THREE.PerspectiveCamera(40, window.innerWidth / window.innerHeight, 10, 1500);
  camera.position.set(-400, 200, 400);

  controls = new THREE.OrbitControls(camera, renderer.domElement);

  scene.add(new THREE.HemisphereLight(0xffffff, 0x080808, 1));

  let objectMaterial = new THREE.MeshStandardMaterial();
  scene.add(new THREE.Mesh(new THREE.CubeGeometry(50, 50, 50), objectMaterial));
  
  let roomShader = THREE.ShaderLib.cube;
  let roomMaterial = new THREE.ShaderMaterial( {
    fragmentShader: roomShader.fragmentShader,
    vertexShader: roomShader.vertexShader,
    uniforms: roomShader.uniforms,
    depthWrite: false,
    depthTest: false,
    fog: false,
    side: THREE.BackSide
  });
  
  let roomGeometry = new THREE.BoxBufferGeometry(50000, 2500, 50000);
  let room = new THREE.Mesh(roomGeometry, roomMaterial);
  room.position.set(0,800,0);
  
  var loader = new THREE.CubeTextureLoader();
	loader.setPath( 'https://threejs.org/examples/textures/cube/Park3Med/' );
	loader.load(['px.jpg', 'nx.jpg', 'py.jpg', 'ny.jpg', 'pz.jpg', 'nz.jpg'], texture => {
  	
    roomMaterial.envMap = texture;
	  scene.add(room);
	  
    //1 Test: comment out these 2 lines -> room cube shader will stop working
	  objectMaterial.envMap =...