Final Cut Pro X Green Line

I have been making a movie with my friends and when i add in some muzzle flashes, by using add then using transform to move them into place, well the transform part is my issue. if i dont use transform and leave the muzzle flash in the middle of the screen there isnt a green line but as soon as i start moving it around there is a green line that appears. the exact location is on the right side and will always stay on that side even if i rotate it. Its the most irritating thing. Ive looked up my issue and nobody seems to be having this particular issue. I even shared it as a file to see if it would go away and it didnt it stays there. and i dont know what to do.