Hi ! I've repeatedly moaned about clunky FBX import in the wishlist, but I've now met a genuine bug.

https://www.deviantart.com/1-neiviesis-1/art/2015-Version-2-Sadira-Genie-805458225

The FBX broke in Paint 3D and PoserPro 11.3, but was okay in Autodesk's free FBX Review. { https://www.autodesk.com/products/fbx/fbx-review requires free registration to download... }

If you use Poser hierarchy to identify then parent each half's multiple orphaned sub-trees with umpteen parts to a dummy place-holder, then rotate the lower, they will align. So, there's a +/- gone astray ?? Of course, given FBX rig import issues, posing is hard...