[TGL-H] External monitor is flashing if the resolution is 4k@60hz.

Connect external monitor to TGL-H platform with mDP and configure it with 4k@60hz.
Play Youtube with firefox/chrome and locate youtube on the external monitor.
The external monitor would be flickering(turns black and return normal repeatedly).
Check the dmesg and got this error
#i915 0000:00:02.0: [drm] ERROR CPU pipe B FIFO underrun

During the external monitor truns black, the error message keeps showing up.

The connector's(DP) status is always connected.

Here's drmtip(20210223) log that change to 4k@60hz from 4k@30hz.
20210223_dmesg_chng4k60from4k30.log