That's a crit and it's common knowledge that crits don't care about what armor you're wearing. Get a bad roll and you're dead.
Roll isn't the major factor why critical hits do so much damage with SD , but bypasses. 1 luck equals to 70% chance to be bypassed and of course when you die by a critical hit that's supposed to be a bypass and it is , it just is shown as a normal critical hit in log. In the end it doesn't matter much what roll , if you get bypassed it's GG.
Or just shitty build/armor/unluck Nothing more
Build if you have low luck , armor if you aren't at least wearing MA Mk2 ( 1/4 less damage is at least something ) and to be unlucky is when odds just doesn't favor you depending on the current chance to be bypassed.

You can have all anti crit perks and best armor vs incoming dmg type and still receive total fuckover crits.
Incorrect , 10 luck - 0% chance to be bypassed from shots in torso , that includes SD too. ( Solar provided chart )
8-10 luck CA with at least 150+ HP and you pretty much survive each critical SD plasma nade hit , with tesla and same amount of luck you can't be taken down even with 3 grenades.
So a plasma tank build with 10 luck , 250+hp and CA is just a hard counter for them.