Causing damage but enemies dont lose HP

Maybe its just me, but in the last 2 weeks of playing I have noticed something very upsetting. Regardless of where I fight I have seen that even though we are striking our enemies, and the damage numbers are coming up, that they dont lose life. This always happens when its just 1 enemy on the screen. 6 or 8 people can hammer the daylights out of whatever it is, and you see the damage numbers, but the health bar doesnt move. Granted I have been in battles where the enemies dont even have health bars, but in this case, they really dont lose health. I can be in borliss pass, fighting a dwarven hammer guy, and he will take all my nukes, and shots twice before dying, and Im lvl 20 while he is, what, 8? This also happens a lot in thirsty river against individual guys as well. Was fighting 1 enchanted swordsman, just one, and it took 6 lvl 20's 90 seconds to drop him. We were, 2 warriors, 2 nukers, necro and monk. He literally lost no life for quite some time, despite the damage numbers flying up. What the hell is this? Then in complete contrast, I lost 541 HP in one hit. One hit? What single skill can do that? I was not hexed, and had no conditions, and this isnt the first time. Does any of this happen to you all?

I know for the enchanted sword that they use Endure Pain, and it sometimes appears as though you aren't dealing any damage to it. That is the only explaination I could think of.

You mentioned the Enchanted Sword enemies. There's a very good reason their life acts so sporadically--they're using a HP increasing skill such as Endure Pain. Once it wears off, you see their telltale hp jump back down and they take damage much more easily. I would suspect the other enemies you mention use the same skills.

You sure there was no monk casting mark of protection?

Single strike death happened to me as well but only once... Lost 510HP.

single strike death seems often to be the cause of a kind of lag

No monks were casting cause the monks were dead. I know they use endure pain, but even when it goes away, the HP remains. This is something I have spent time watching over the last 2 weeks. I have made sure that other factors, i.e. monks or endure pain, are taken into consideration. The only thing I can think of for the enchanted swordsman is them casting endure pain every 10 seconds, which shouldnt be possible. I know in many cases I have been slammed by distracting shot, from 1 guy, multiple times, as if the skill has no recharge time. Thats another issue. Anyway, no monks or other outside forces are helping these enemies live, and they are... Why? And the 1 hit death thing should be impossible shouldnt it? Lag taken into consideration of course.