My Acer Aspire V3-572G started doing this about 4 years ago after the fan failed while gaming. Didn’t really notice it for a while other than when It was really cold, because it heated up fast with no fan. Also, the GPU is further away from the heatsink than the CPU, so it got hotter quicker. Once I purchased a new fan a few years back the lines on the screen stayed for longer and longer because the fan was keeping the GPU cool. I use this computer for school and it is very annoying, as it lasts about half an hour, and when unplugged it uses less power to save battery = less heat.
About the battery saver, when unplugged, the laptop switches from 840M to integrated graphics, but it doesn’t seem to make a difference.
I think it is a cracked solder joint on the chip, and I checked the internal cable connector but it was fine. Flexing the entire keyboard or the screen makes no difference. The lines do not appear on an external monitor, so I am on the fence whether it is a monitor or GPU issue.
Yes, the laptop is 7 years old, and i think it needs to retire. (writing this from the laptop)