Thank you for your comment. I'm not familiar with Unity, so I don't have a direct solution for you, but would the following thread or something similar be helpful?
Unity 2D art is blurry - Stack Overflow
https://stackoverflow.com/questions/43317931/unity-2d-art-is-blurry
Also, since the image causing the problem is vertically long, you may want to try splitting the image in Photoshop or Gimp to a different size. Changing the state of the image may reveal the cause of the problem.
