Built-in handicap for assassins?

[VisionAndVoice]

This thing happened today.

I went solo to Derelict Defence, and it was the second wave when Stalker arrived with a visit. I didn't bring my good gear so I couldn't take him head on while defending a pod, so I decided to evade him for now and deal with him at the end of the 5th wave when Infested would run out. Plan worked, eventually we were left one on one and a proper fight started.

But after a while I noticed that his attacks stopped inflicting damage on me -  I got careless and caught a couple of his sword waves with my face, but was unhurt. And again, and again. Eventually I decided to just rush him and indeed, he was hitting me dead straight, but I did not take any damage from any of his attacks(sword, grenades etc.) nor even flinched. I know that at the beggining of the fight he could damage me, as I had to eat some consumables after he got me once, but in the end he just stopped hurting me with his attacks.

Another similar thing comes to mind after this, this time with syndicate kill squads. On several occasions when they cought me off-guard and I was underequipped I had to evade them, and then after some time passed when I was ready to fight they did not fight back at all, just standing there or walking around but never returning fire.

So what I'm really asking here is - could there be an inbuilt handicap for assassin type enemies that activates if you've managed to stay alive long enough without killing them? Kill squads stop attacking, Stalker stops dealing damage, possibly others... Did I just catch a lucky glitch, or is there a feature of an inbuilt timer for a handicap, so that if you can't beat them straight you could simply outlast them?

Does anyone have an experience that could clarify this?

[Babellon]

I think that qualifies as a bug to be honest. I'd say screenshot it next time if you can and report it to the bug section regardless. Stalker and his latest cohorts should be doing damage regardless.

[FINNSTAR7]

I've had the same thing happen to me with the Syndicate Assassins. New Loka sent in their stupid Ancient Healer Eximus units and I thought I was screwed, but when I came across them they simply didn't attack me. It's happened several times but I think it's a bug, not something purposeful.

[Ikusias]

Seen the Ancient's thing happening a fair number of times, it's probably due to the extremely crappy AI all png possess: if you get out of their aggro range for long enough they become unresponsive and easy to snipe to death