iMac 21.5 Mid 2011 Display Pixel Flicker

Some month ago i bought a used iMac 21.5 Mid 2011. And since then there have been coming some wierd pixel flickering on my display. It's not dead/stuck pixels, they disapear and then a second after they comeback, etc.

I have had it to rep. at Humac and they have changed the Logic Board and the Display.

But i still have the issue, much more than before i send it to Humac!

I have also recorded a video of it:

https://www.wevideo.com/view/88536822

Please watch it to the end!