Okay then, here is a basic Rig with a Blocky Mech Mesh to show a possible way to set up a Mechanoid Character Skeletal Mesh from Blender to UE4. I have successfully exported this rig and mesh and anim to UE4 with no issues. It has basically the same animation and functionality as Nightfalls original Skeletal Mesh, but without the issues.
This rig has an Inverse Kinematics constraint on both legs and I have added a joint in the main body so that the head doesn’t wobble from side to side.
The feet have “Inherit Rotation” unchecked so that when their parent bones rotate from side to side, they retain their upward facing direction.
The animation itself is not perfect, but similar enough to Nightfall’s original anim, as to illustrate a working rig.
Heres the Blend: MechPrototype_Complete.blend
Hope that’s helpful! 