Why is this still an issue? I am having this problem, the retargetter cant even properly retarget UE5 manny to UE5manny (himself) without the same issue. best option I could maybe find is this plugin that forces the IK to snap to bones, but why should I have to pay for something that has been broken in UE5 for almost year now?
https://www.unrealengine.com/marketplace/en-US/product/rm-fix-tool?sessionInvalidated=true