Assuming that your swg salinity reading is 500 ppm lower than actual, your cell is beginning to underperform. As the cell gets older, it will read lower than actual. Once it reads about 800 to 1,000 below actual, it's about time to replace the cell.
The lights are due to the swg thinking that the salinity is 2,700 ppm or lower. Raise the salinity to where the swg reads above 2,700 ppm and the lights should go out.
Get the Taylor K-1766 salt test kit to monitor your salinity. Once the swg reads 800 to 1,000 lower than the K-1766, replace the cell.
What are the readings as you push the diagnostic button?