I had this issue while updating the system version.
The story goes like this.
I need to update my system. The machine has been bugging me to update for weeks.
I remove external monitor and power
move laptop to other room. Closer to WiFi.
I start up ate. It seems to proceed OK.
About twenty mins later the screen is black
I restart the laptop.
I get the pink lines
restart again. I get the system updating loading screen
twenty mins pass. I see this string about the pink lines. I think is have a video issue. I’m planning a trip to the &&^&^$^ apple store
I move laptop back to the other room plug in external monitor and power
Loading screen appears on external monitor with some time left on the up load
The upload completes
i get normal working screens on my laptop and external monitor !!!
im not sure what happened. Perhaps I caught the updating in mid update so it showed the pink lines. Not sure.