Humanoid rig not animating additional prop bones correctly, but Legacy works fine
(Generic also works as expected)

When importing a Humanoid Model & Animation in separate files, resulting hierarchies are different because the "animation" files get their top node removed (single parent node), while the rig/model file keeps the top node because it's not a single parent (skeleton root + mesh root)...

in consequence, the animation is not mapped properly to prop/extra joints since the joint is not found where it's expected in the hierarchy.
see attached gif...

We should handle this case properly, as the user originally created two identical hierarchies, with the exception of an additional mesh root, which is normal/expected practice.

repro:
-import attached 810165.unitypackage into a new project
-open phoneJointScene scene
-expand/search hierarchy for...
... CMR:R_WeaponAttachMent_jnt & CMR:R_WeaponAttachMent_jnt joints
-compare rotations... identical.
-click the Editor Play, then Pause...
-compare rotations... 90' difference between the two. This is caused by the animation not being applied to this joint.

-open comparison scene
-expand both roots...
notice the difference in hierarchy...
"Biped:CMR:root_jnt" joint is not at the same level of the hierarchy.