I have heard that high phosphates can cause the cell to stop producing. I believe that calcium phosphate coats the plates but cleaning the cell is supposed to get it working again. I have ove 1000ppm phosphates in my water and my aqualogic is maintaining 4 ppm with the output set on 8%. I do know that high pH can inhibit production.
Have you tried losening the union at the cell and collecting water from it and testing it for chlorine to see if it's producing?