Monitor is flickering when connected to a dock

Hi ,

I have a Latitude 7490, and WD19 Dock, and dell qhd monitor and benq FHD monitor. 

when i connect both the monitors to the Dock, I am facing two issues.

Either both the monitors resolution set to FHD or one monitor is working at qHD and the fHD monitor is flickering horribly.

I had changed the HDMI cable to DP cable and both the monitors to DP cable, still the issue is coming. 

Thanks in advance

please