Unity AI FPS problem

Hi, i have a problem with the Unity FPS tutorial. I have taken the AI robots from it for my game, a top-down, twin-stick adventure game, and i have set up the Rocket Launcher from it so it is moved and aimed with the mouse on-screen, so you point where you want and shoot a rocket.

The problem i have, is that i have set up the robot AI the way it does in the tutorial (by setting waypoints for it to follow) and it works fine for around 30 seconds after the game starts (meaning the AI follows the path and i can kill it) but if i was to wait for 30 seconds or so, it won't register my shots on it anymore, and starts jittering about along it's set path, still moving, but no longer responsive to my actions.

Would anybody know a potential reason for this?

Thank for any assistance.