1) What happened
On the Animator component, clicking the Optimize Transform Hierarchy button with multiple gameobjects selected only works for the first selection.

2) How can we reproduce it using the example you attached
Open a scene with duplicates of the same animated humanoid avatar gameobject.
Select all the animated gameobjects.
In the inspector, under the Animator component click the Optimize Transform Hierarchy button.
Note that this only changes the hierarchy for the first selection you made. Others are not affected.

Apologies for lack of example project, the bug reporter wasn't working.