U2718Q, Firmware M2B103, keeps switching to YCbCr422

I have 1080Ti

It's set up to be RGB 4K 10bit Full Output dynamic range.

Sometimes when I start the monitor, it's switched to YCbCr422 and displays very jagged text.

I am not using the provided 1.8M/6FT DP to mDP cable. I am using a longer DP cable. Right now, I have switched from long DP cable to another shorter DP one. The problem has not yet appeared for 2 days.