The author really ought to make this more clear: Immersive animations sets one animation for a weapon type. The weapon types are: sword, axe/mace and dagger. This means, whether you use dual wield or 1 handed and shield, it will be the same animation. Skyrim by default does not have separate files (that is why the shield is on the wrist in vanilla). The solution? XPMSE. With that you can change the sheath location of many weapons, and the animation will follow the new weapon node. This means you can dual wield on back, and then pull your shield, with the right animations. However, a bit of reading anywhere else online would have given you the solution. Lots of people not reading instructions, it would seem.
