Post Deleted
Have you searched for a solution here on the forums? This seems to be a common issue - parenting an object to a hand bone - to be able to follow the hand.
Search / Look up - weapon change - or fps weapon change. You should find a solution to this issue.
If not - update this thread and we can proceed with troubleshooting your workflow.
This is interesting
I would assume just using a empty game object as a root for any object would be alright even if that object will have multiple bones - like a whip or mace or something similar. Then I’d also have an empty game object or a null/dummy object located at the palm area - parented to the hand bone.
Then I would parent the weapon go to the hand/palm go. I think this would work - though I have not had to perform a setup like this yet. Programmers have done that part in engine. 
May consider that simple setup just to test - would be good to have empty game objects at the hand - so every weapon would parent and orient correctly each time - and have an empty master root for each weapon that has multiple bones - so not to mess up the hierarchy of the weapon/object.
i had some strange behavior a while back too. The problem was the orientation. Maybe you check the orientations on your shield, check the ones for sword and such, which work already, and see if that’s your current problem.
If the shield isn’t the problem, check the bones. In 3Ds Max it’s always a good idea, after linking, to reset transform and scale. And also freeze transform stuff, before creating constrains and so on.