I have restart my game a few times due to the fact that i go in to a lair and never see the spawnery even after running the entire map and checking every nook and cranny. Im not sure if it spawns after a certain amount of kills or whatever but it seems to be easier to let to evolve to a citadel where i can definitely see the scylla …its abit frustrating for me to waste an hr in a map for no reward in terms of research or whatever. There is also a bug i find where if I hire a soldier and put his gears on a higher lvl soldier i lose the gears, and im sure i didnt scrap them so just a few things to look into
Look to the far right or left of the maps. They are in a square pit. Normally you have to be looking down into them to spot it, though sometimes you get lucky with a distant view if the barrier gap lines up just right. Another good trick is to jump to the occasional high ground pillars. Their higher level tends to assist at times (again, if lined up).