Error "Multi-root BVHs not supported" in ShaderMaterial

Questions
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1

Hi all !

Please help me to understand the reason for the following error:
Uncaught Error: MeshBVHUniformStruct: Multi-root BVHs not supported.

It arised when I switched from geometry, produced by OBJLoader, to BoxGeometry in custom ShaderMaterial. Simplified code that use this geometry is following:

const makeGem = (scene, env, camera, res, geo, {
  color = new THREE.Color(0.1, 0.2, 0.01),
  ior = 1.8
  } = {}) => {
  const mergedGeometry = geo;
  mergedGeometry.boundsTree = new MeshBVH(mergedGeometry, { lazyGeneration: false, strategy: SAH });
  const collider = new THREE.Mesh(mergedGeometry);
  collider.material.wireframe = true;
  collider.material.opacity = 0.5;
  collider.material.transparent = true;
  collider.visible = false;
  collider.boundsTree = mergedGeometry.boundsTree;
  scene.add(collider);

const gem = new THREE.Mesh(geo, new THREE.ShaderMaterial({ ...
});

gem.material.uniforms.bvh.value.updateFrom(collider.boundsTree); // Error here !
...
);

Online test is here.

I understand, that question is very specific and maybe provided information is insufficient,
but I am a new BVH, so any suggestion at least where to look will be a great help !

2

Although the reason for this error is still a mystery to me, I found a workaround by processing BoxGeometry with Manifold CSG first.