I had exactly the same issue. Initially 1 vertical bar of about 1.5 inch wide, later 2 bars and sometimes when you move the screen it was gone for a second and came back mostly. I found that it was the LCD screen and bought a LG replacement on ebay for around 90 euro. I replaced it myself following online guides as Apple wanted to replace the whole lid for approx 400 Euro. System is now fully functional again for 6 months without any further issues.