Test done and shapeshift works with off-hand weapon:- No more laggs
- No more crash
- with only some version of shapeshift (see file: https://www.mediafir...6h1c3lkwu/shape), if you equip/re-equip a shield, AC bonus stack until AC=-20 and stay after going back to human form; AC bonus can't be removed by usual ways after that.
I had this lag problem (I'm playing version 4.0 of Improved GUI) when changed into drow form in the Underdark and later during The Darkest Day questline - any shield/weapon in the off-hand made the game unplayable. As for the AC stacking, I get this when changing armours/robes while holding some shields (but not all, it seems only bucklers), but it gets back to normal after reload.