Testing Requested: Reinforced Shield bug?
By chance were you in a area that you were downleveled? I know for things like engineer juggernaut trait that is supposed to give 200 toughness when wielding a flamethrower is not actually giving that amount when downleveled which makes sense. Just trying to rule out any possible obvious things before really looking into it.
Edit: I suppose I should click links before asking lol
It was a minor trait causing me to lose 100 toughness when my health went under 90%.
My bad!