Maybe this is the problem, followers hit with marked for death will permanently lose armor. I've found the solution for that, you just type on the console " getav info damageresist " then at the end it tells you the damage is -1600 in my case was -1500 you just have to type restoreactorvalue damageresist <number> if your damage is -16000.04 you type " restoreactorvalue damageresist 16000.04. Hope it helps!