I ran into an issue while attaching a mesh to a bone in the player character with the player character loaded from a gltf file. Attaching meshes to bone worked fine when a similar character was loaded from a .babylon file. The gltf file was exported from blender.
Anyway, here is a playground example to show this:
Note that the red sphere is supposed to be attached to the character’s right arm when you press the key “p” on your keyboard. But the sphere simply vanishes - nowhere to be seen.
Give it a few seconds to load the playground as the mesh is loaded from github and may be bit slow first time.