Firstly detect that LOS is working and they are indeed seeing each other, you can set up so the object is destroyed to confirm this. If they are not seeing each other, be aware that the LOS has a cone of view which may not be pointing towards the other object and so they are not in the detection area. With the turret just looking at the enemy and not moving at all you may be triggering events once only instead of constantly checking so look into this. Take a look at the tutorial level for turrets to see how they are set up.