Yellow grid squares display on my mac

I brought my computer in about a month ago to fix a logic board.

I got it back and I start to observe some sort of yellow grid of squares display on my monitor as well as on external monitors that I connect to (different monitors, with different cables).

I brought the macbook back into the shop twice, the first time they just removed a system, saying it's know to cause the problem. The problem persisted so I brought it in again the second time, upon which they supposedly replace the mother board again.

I just got it back and the same thing is still occurring. These squares appear randomly, of different sizes and different locations on the screen. They quickly disappear upon a mouse touch so it's hard to capture them.

I've attached some pictures.

If anyone else has experienced the same thing or has an advice on what I should do, I would really appreciate the help.

This one is with a Samsung external monitor

This one is on an AOC monitor

This is on the Mac itself.