Why does the obj file look different in ThreeJS online tool?

I use open3d to resample pointclouds in bunny data, then construct the mesh.
But it looks different from the original bunny(some empty face) in ThreeJS online tools, more details can be seen in this issue (Why does the bunny I save look different in threejs online tool? · Issue #4590 · isl-org/Open3D · GitHub)

    Some files are uploaded.

    1. bun_zipper.ply: the original bunny file.
    2. bunny_zipper_save_obj.obj: read bun_zipper.ply then save into obj files
    3. bunny_sample.ply: read bun_zipper.ply then resample points and contruct mesh.
    4. bunny_sample.ply: save into obj file

bun_zipper.ply (2.9 MB)
bunny_sample.ply (277.0 KB)
bunny_zipper_save_obj.obj (2.4 MB)
bunny_sample.obj (491.0 KB)