I have a similar problem. I get the following error message when loading a gltf file with the QML SkeletonLoader:
[Qt][Qt3D.Renderer.Jobs][2] :0 :: Unknown buffer 0 when processing buffer view
Neither self-exported files from Blender nor files downloaded from the gltf git (glTF-Sample-Models) are working.
So I also need to know how to correctly export gltf or whether further adjustments in Qt are necessary in order to make it work.