Having a black line in the middle of the screen while playing on imac resolution 2560 x 1440

I opened my game, there was a black line along the middle, no it's not my Imac's problem.

Going in water or going behind trees and mountains seem to be find, It's the sky behind the blocks ( Trees and Mountains) that are having problem.

How to trigger: Just open up the game on a Imac on a 2560 x 1440 resolution.