In case you’re wondering why I suggest changing the unit scale in Blender, Unreal appears to scale static meshes and skeletal meshes differently.
A static mesh can be exported just fine with a Blender unit scale of 1, since Unreal knows to automatically scale everything up by 100 (Unreal base units are 1 cm, whereas the Blender base unit would be 1 m).
However if you try to do the same for a skeletal mesh, Unreal doesn’t automatically scale the skeleton properly and you end up with a mismatch (1 blender unit becomes 1 unreal unit, so 1 metre becomes 1 centimetre and the bone positions get scaled down 100x).
I set the unit scale to 0.01 in my default Blender startup file, so I can do both skeletal and static meshes and don’t have to worry.