EDIT: This was originally split off from the Handplane3D thread requesting a UE4 preset for Handplane. It's now discussing some apparent faults in the way UE4 calculates tangents on imported FBX files.
I think that's probably because UE3 is (still?) unknown in terms of tangent basis so Handplane was close but not quite. UE4 has a clearly defined tangent basis.
Personally I'd prefer to use Handplane over xNormal's obj-to-tangent converter tool as Handplane's much faster and easier.