Hi all. I've been playing the game for a while now but took a break so I only just started playing again recently. Got a medium sized prison going. I've been getting multiple signals from my patrol dogs about tunnels so I've been searching the toilets more or less every night for about six nights, but the guards found nothing. Then all of a sudden I got six escapes from an absolutely enormous tunnel network. Why didn't my guards find the tunnels despite multiple searches of all the toilets including those from which they started? Is this new in the most recent version, that they have a chance of not finding them, and I just got really unlucky? Or is it some other mechanic?

Thanks in advance.