Can you try to export from Max to .obj / .fbx / … (I don’t know the export formats supported by Max, but you should choose a format that support skinning) then from this format to gltf and see how it goes?
If it still does not work, that would suggest the problem is not with the exporter but with your model.
Also, did you try the gltf file in another gltf viewer (like https://gltf-viewer.donmccurdy.com/), just to be sure?
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Another thing: are you able to provide a PG the displays your gltf file? That may help to dig further.
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