The option 'General - Optimize render performance' limits the number of chart objects to be rendered on the screen. This helps to control the rendering time of the chart so your CPU/GPU is not overloaded and charts are still responsive. But you may see chart 'flashing'.
To avoid excessive flashing:
1. Adjust 'Maximal render time, ms' parameter, increase its value.
2. Turn off 'General - Optimize render performance' option.