I would suspect that the LCD is damaged. It could be just a small tear in the flex, damage to the connector or a logic board issue.
If you have access to a known-good Air 2 screen assembly, then you could use that to eliminate an important variable. Unfortunately, the Air 2 screens are in short supply and very expensive.
Start by inspecting the flex and connectors under magnification, then move onto the logic board, specifically the area around the LCD connector to see if there are any dislodged components.