When you wake up a room full of Z's, you back out and stealth out. If you manage to get far enough away with obstacles in front of you, your nifty meter says unseen. Wait long enough and they will forget you and start wandering at random.
When you’re wearing T6 assassins amor they should forget you almost immediately. Not anymore, they haven’t forgotten you. You don’t get the stealth damage bonus and as soon as you shoot one, the entire crowd comes at you. Perhaps it’s the T6 that’s been nerfed. There’s a time element in this that gets shorter as you go up the armor tier and used to be almost instantaneous with T6.
Whatever, it's broken. I don't recommend upgrading to this version if you use an agility build.
The youtube posters who made videos about an OP build got what they wanted.