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Multi-primitive morphological bond gltf problem - Questions - Babylon.js (babylonjs.com)
May help you.
Babylon splits the primitives into meshes, and the shape keys are split with them.
As in the example in the first address, if you look at the object tree, you will see that all six faces of the cube have a complete set of shape keys and have the same name.
If you only find the shape key with the corresponding name under one of the meshes to animate, there is likely to be a problem.