Regarding the model's UV issue

According to GLTF Specifications -

Client implementations SHOULD support at least two texture coordinate sets, one vertex color, and one joints/weights set.

Babylon loader supports UV3 - GLTF2Export.GLBAsync can't export uv3 uv4 - #3 by bghgary , not sure about the exporter current state.

Seems that the problem relates to the export from 3D Max. Could you share your original file to have a look?

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