After we put in the 4 24 inch screens that can rotate to Portrait, we found that we wanted one to stay landscape while all the others to go portrait.
The best way to do that is to NOT install the HP “My Display” software that senses that you have some of your displays as landscape and some as portrait. If you do that they sense the rotation and will blink…… and blink……and blink…….and blink …….and blink ……….and blink and …….
You get the idea. If you just let the nvidia card control the rotation and not have the HP software do it, it works fine.
Moral of this story is that sometimes you DON’T want to install all the software that comes with the monitor.