On page 14 datasheet, there is the description about setting OVP level. "Do not set the OVP level higher than 3V above the maximum LED operating voltage. This is only required if your DIM signal crosses the 5 or 6 oscillator clock cycle boundary as described on page 14 of the datasheet, the control loop of the MAX16838 experiences a discontinuity due to an internal mode transition that can cause flickering.
To avoid flicker, the following is recommended: Do not set the OVP level higher than 3V above the maximum LED operating voltage. Also, optimize the compensation as shown in the datasheet to minimize recovery time