It's not the controller the connection between the lights is only a 0-10v signal and it's not going to die off only 3 lights down. Are you positive all the lights are exactly in line, exactly the same height off the water and are all exactly straight up and down on all axis. Look down the tank length wise and be positive that last light lines up exactly as the rest. Once your positive they are all positioned the exact same. Try using shorter link cables if your using the super long ones kessil provides. The link cables are literally only AUX cables go buy some short AUX to connect between the fixtures. I'm suspecting that last light is facing forward a tad bit. Get a short level don't just eyeball it.
If all that doesn't work contact kessil and trouble shoot with them they have great customer service and will take care of you however the must.
