Hello, thanks for the detailed feedbacl!
About the lagging and the passing through guards, I believe this is due to a mix between your computer maybe being a bit slow and my very unoptimised game, and also the way that I move the player. Each spacebar press moves the player and the enemies and if the framerate drops and you move enough update wouldn't be called to check if the player and the enemies collided.
And about the AI, yes, I totally agree, I don't know why I was thinking that this would be enough. In fact it is not based on probabilities, to make it consistent (again, should have explaines it more clearly).