I needed a parent that would give me control over both hands, and continued to animate the gun object and its children using constraints. I ended up with the desired animation, but when exported, the gun oddly enough is offset halfway the animation.
It's another one of those things that feels like it defies all logic.
Is there a way to change the parent of the gun to the right hand and keep the animation intact?
When things are parented to the hands, I guess things work better. I did not have this problem with another reload animation and the gun was parented to the hand there.
This was a hassle but doable since I was still in the blockout phase.
In the Scene:
1. Duplicate your character (in the hierarchy) as a backup.
2. Change the object to the hand as the parent.
3. Give the object the right start/scene- (local) position to prevent offset.
4. In config, select "Apply Scene Pose".
5. In config, create the same setup for all the child objects to have bones.
6. Remove all the keyframes onwhich you applied "Update Position and Rotation keys".
7. Re-add all constraints on the keyframes you previously started constraint connections on.
This fixed the offset and now results are consistent.
For now I am wary of parenting to anything but hands with humanoid animations.
Customer support service by UserEcho