If you clear it once, they hide. If you clear it twice, they move. After a few runs, patterns show. Web density. Spawn points. The kind of things you only notice when you are tired and paying attention anyway.
You actually did it. Five clears, and you're still in one piece. The entrance already looks better. Less webbing in the air. Fewer skitters on the stone.
I am not saying it is the cause. I am saying I have seen stranger things in cracks after a tremor. Keep your eyes open down there. If you see anything that looks wrong, do not touch it with your bare hands.