imported skeleton's bones always offset by one so wrongly labelled.

Hi. Im an ubernube here but I have experience with Blender and Unity. I am climbing the walls trying to import my character from a Blender FBX file into a 3rd P game. UE insists on renaming my bones despite my skeleton’s hierarchy being identical to its own manequin’s. It always makes the pelvis into spine_01. Always! Why? I’ve added a parent bone and named it Root. Everything is hierarchically identical to the mannequin’s skeleton. I’ve tried exporting the rig without this extra Root bone and instead named the armature ‘Root’ but the same result. What ever I do…the same result. This offests all child bones. It obviously is to do with the root but I cannot find a solution. Anyone? Pretty please? (I’m also uberpoor so it has to be Blender). TY.

Do not rename the armature. It has to be labeled Armature.