What determines bone hierarchy/bone index?

Hi, guys~~I met a problem related to bone hierarchy in skeletal mesh. When I import a rig into UE by fbx.

Hello @ChristoLiu and welcome!
Please share screenshots and more information!

The only I do know at this moment is you have a “problem related to bone hierarchy in skeletal mesh”

I have not a single clue about how to help you…

Software you are using, how it looks, names of the bones, options to export and import…

At the moment I can share this to you…
https://docs.unrealengine.com/4.26/en-US/WorkingWithContent/Types/SkeletalMeshes/