Fuck sake, those 4-legged machines are a right pain in the dick.
I'm in the Biolabs section, after you drop down the hole and go thru the sewers, you get to a big room with a sentry, one of the fast enemies and two of those robots. I killed the first two enemies and decided to pull one of the 4-legged gits into the previous room. Just one of his attacks is almost a 1HK but I managed to kill him or so I fucking thought, I went back into the room and saw he had respawned.
At first I thought it was the other patrolling robot so I fought him again, he had only a sliver of health left and then disappeared before my fucking eyes. I went back into the main room and, low and behold, he had respawned at full health again!
Seriously, once you pull the enemies you only have a certain amount of time to kill them or else they respawn in front of you at full health! WTF, am I missing something?
I closed the game out of frustration, what a horrible gameplay feature.