Bug Unity 2019.3 Mesh Import Settings window is broken

Recently I noticed that the skinned mesh import window is broken in 2019.3 versions (the "brokeness" varies from various versions, in one of the older versions the unity would show a lot of errors when clicking on the asset).

Currently I upgraded to the latest 2019.3.12f1

I have created a test mesh with root motion and exported it into Unity.
This is how the rig section of the import setting looks:

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Notice how there's no way to select a root bone or no "Optimise Game Objects" option. But change the "Animation Type" to "Humanoid" and we get "Optimise" option:

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Now, if you change "Animation Type" to "Generic" again (which is an animation type that I need for my meshes) we suddenly get all the options:

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This is a quite a weird behaviour, it doesn't look like it's the intended way to edit a skinned mesh settings.

Also in 2019.3.10f1 the Animation tab doesn't display Root Motion controls on animation:

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(note that the root motion is selected in the Rig tab and the mesh moves with a root motion inside a preview screen, though in the wrong direction - upwards instead of forward)

In the 3.12f1 it seems to work correct:

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But the interesting thing is that when I upgraded the project, the mesh that I exported on 3.10f1 still didn't have Root Motion controls. I exported the same mesh under a different name and the Root Motion controls appeared and they are working as expected (they were glitched in 3.10f1, the mesh was moving in the wrong direction)