Typically this is either an issue with the cables which run from the TCON board to the display. Or an issue with the TCON board itself. Sometimes, you can get the machine to behave if you only open the lid a little. This typically points to a cable issue.
Sadly these cables are not easily replaced, or repaired, so the most likely solution will be replacing your screen. Did you pay Apple for the repairs that you just had done? Or is your machine covered by AppleCare+? There is a possibility they may cover this under the 90 repair warranty they offer if your repair was paid out of pocket, but typically that only covers the parts they replaced. And they would not have had to remove the display for either of the repairs you had done. Definitely covered by AppleCare+ if that applies.
I would recommend connecting it to an external display just to verify it's still showing an image as normal. But I expect that will work properly.