The problem is if you are outside the circle on the first hack attempt, every time you try and re-hack the security at that terminal, it just doesn't work. After the timer counts down, even after you defeat the waves and are within the circle, your character just says you'll need to try it later.
The workaround is to leave the planet and come back to this location. Unfortunately you will need to re-fight the initial scavengers at the Flophouse entrance again, but when you get back to this point, if you stay in the circle on the first attempt, it will let you proceed and unlock the boss headquarters for your final assault on the Flophouse.
