@Hoaxx Are you sure you have the World Space set up to Z-up before importing the Manniquin.fbx? Having it on Y-up before importing the Epic skeleton will cause a bunch of weird error like bone rotated 90 degree and floating animation. Changing World Space doesn’t work once the mesh+skeleton has been imported.
I also have Advance Option->Axis Conversion->Up Axis = Y in the FBX export, not sure if that would affect anything.