You can edit the files in the Blender's installation folder. I got the code from the Blender installation and started to search for the places (hierarchy and keyframe) we need to modify. The animation import problem is on top of the image and the correct animation frames position is on the bottom of the image. This causes the animation to have a 'hiccup' when we need to export it back. When we import from the current FBX, the importer adds 1 to every keyframe number on the Blender's timeline. This image below shows the original model from Mixamo on the left side and the exported model from Blender default FBX exporter. And the original exporter just exports it as it gets from the API. The 'Armature' is part of the Blender's data. This is not a fault of the original developers, because the Blender's API exposes the struct the plugin uses to export. This causes the Unity native root motion to stop to work. Worst: when I turn on the 'Key All Bones' option in the current FBX exporter (2021), it creates an animation curve for the 'Armature' (the undesired root bone). This is incompatible with the Unity animation system, because the other animation files need to match the bone hierarchy. The model I export is different from the model I imported. u3d exporter is now more stable and works on every platform removed support. When I tried to export only the mesh with the rig, I got an additional empty root bone in the hierarchy called 'Armature'. You can download in the download section, or in the github release page.

I made the modification in my Blender's installation and now I'm sharing the code here. When I was dealing with exported animations to test the plugin I developed, I discovered that the Blender's exporter comes with two limitations: It does export a ghost root bone called 'Armature' and it does import one keyframe ahead of frame 0. FBX exporer from unity packages with this config: Steps: Importing this asset into Unity Target scene object from Hierarchy tree - right click and Export to Binary FBX format Importing FBX file in blender, and the result is that There is no terrain, nor textures, only some colors here and there. Very recently I developed a plugin for Unit圓D to deal with animation root motion. Custom Blender FBX Format Importer/Exporter

Fbx exporter unity github