Why this happens and a way to fix it [Animation]

[Malfatto]

Hello.

I've experienced this thing with modded weapons where when you use VATS, the left hand of the character is off the weapon, he then proceeds to hold it. It depends on the weapon, in some cases it happens once since the game started and in others everytime a save is loaded.

I tried in 3DS Max matching IK/FK, adding link constraint, but it didn't work. I'm not skilled in 3DS Max either so there is not much I can think of doing.

Does someone know why this happens? Is there a way to fix it?

Here is a video showing what I'm talking about:

Thank you very much.