Cannot understand the rotation of a mesh attached to the socket of a scaled mesh (Z -1)

[Bozarre]

Update

I tried to mirror the mesh in Blender and export the Skeleton and The SK Mesh as LeftHand and I have some a very weird bugs:
In the Physics Asset the collisions looks alright

But in the Scene, with the collision debug, it’s all messed up
And it’s the same with the sockets
In the Skeleton editor

In the scene

WHY !?