I am currently on a kill-all-authorities playthrough, Golden Cat mission. I dispatched all guards on Clavering Bulevard and Holger Square and rewired both the Wall of Light and the Watchtower. Then I went into Galvanni's home, and when I came back out, there were 5 new guards there, coming in from the tunnel to Holger Square. I killed tham, too, went into the Art Dealer's home and when I came back out, the exact smae 5 guards again came in from the same tunnel...

Edit: Same mission. I went up the stairs to the top floor of the Golden Cat and I was suddenly detected by two guards behind me. I reloaded and went up the stairs backwards and sure enough, the two guards appeared out of thin ai right before my eyes...