Screen Problem

It could be a graphics problem, but the graphics on these are built into the i series processor, so I would be more inclined to think it was a display cable problem. I used to have problems like that on a 2009 unibody macbook where the display cable would send funky signals every so often and then eventually it would only work when the display was at certain angles. Hopefully that is not the start of bigger problems, but keep an eye out to see if it changes. Another thing could be faulty video signals after sleeping, and a restart or SMC reset would clear all that up

 

Have you tried moving the screen in different angles to see if its a connector problem and if that doesn’t change you made need a mother board replacement which is $800 better off buying a new mac at that point

 

Probably a GPU issue. Seen it before with VRAM being corrupted. But if it works fine on a TV, probably it's an issue with a motherboard/screen connection perhaps coming out at times partially.

 

Extremely unlikely to be a GPU issue since the GPU is on-die with the CPU and there's no dedicated VRAM, it's all main memory. So if the GPU/VRAM goes south, probably you'll have problems with the CPU and everything else too.

 

I used to have this problem on my other laptops. I consulted a laptop repair person and he told me that this happens when the display cables get hot.