Thanks a lot for sharing your model.
I did a few checks and found that FBX is actually carrying invalid data (as expected), and also that this invalid data is also in the Blender data.
This invalid data could have been generated by a modifier (maybe skinning).
Surprisingly, it works when you upload directly the
.blend file (for this sample at least) but I guess we’re just lucky with this one.
I would recommend uploading the
.blend file directly instead of using the
.fbx export since it adds a step where issues can occur.
By uploading the blend file, if anything goes wrong we are more easily able to debug and provide info and workaround.