I can't remember if the Torment originally have health regen abilities (even though I wouldn't mind) but there is an issue where you will drop an enemy's health completely and they won't die. It's a strange bug where when this happens they will become invincible for a random amount of time even though their health is at 0%. If I continue shooting at them while their health has already dropped they will not die at all, so I have to stop shooting them, give it like 1 to 2 seconds sometimes more and then shoot them again to kill them off. Another way it can happen sometimes is they have to regen their health to take them out. This bug has been around for a while and still has not been fixed.
Edit: Seems like the problem can be bypassed if you switch weapons then they all of a sudden become vulnerable. This needs an immediate fix as it tends to mess you up at the worst moments when you should have been able to kill the enemies a long time ago.
Edit: Seems like the problem can be bypassed if you switch weapons then they all of a sudden become vulnerable. This needs an immediate fix as it tends to mess you up at the worst moments when you should have been able to kill the enemies a long time ago.