For now, retargeting is broken on 5.6.
Even if you export the third-person SK mannequin from 5.6 to reimport it under a different name and then try retargeting on the SK mannequin, thus using the same names on both sides, it won’t work. You’ll get this error message: “IK Retargeter bone chain, Root, was unable to be normalized. Chain too short.”
I tried this after cloning a project and found that all my animations were broken, since even those that had been retargeted on a previous version will be broken again at the hand level.
It’s currently not possible to use these functions, at least I haven’t found them yet; I think we’ll have to wait for a patch.