White lines like that are errors in the data. They can appear when we transfer the retinal slices into the computer program. Some data errors are easier to trace around than others so just try your best to go around it,
If you have issues in the future feel free to post the cube and we can help you out.
you can also use alt+left click+drag on 2D to change planes, the white line may or may not exist in other planes in the same cube.