Ok I found the root cause 
The way we handled skeleton within glTF was a bit too convoluted in 4.2
So we decided to simplify it a bit. From the breaking changes of 5.0:
https://doc.babylonjs.com/whats-new#breaking-changes
Loading glTF assets with skins now places skinned meshes as siblings of the corresponding skeleton root nodes instead of using
skeleton.overrideMesh
(@bghgary I think we should document that and how it works in the skeleton documentation)
Here is the fix for your PG:
GLTF character bone positions | Babylon.js Playground (babylonjs.com)
The idea is to figure out which transformNode is the root of the actual mesh