This has happened to me. In my case the map would look fine when I closed it but then when I reopened it or modified the layout, the green lines would appear. Always two of them.
I have managed to create a (4th) version of my map that the green lines have yet to appear in. I took everything off the page layout (ie. scale bar, compass, text, border). Then, using the select tool, I drew a selection area over the entire map. When I did that, I discovered two little-bitty blank boxes at the bottom right of my page. I deleted those two boxes and re-inserted everything from scratch. I don't know for certain that the boxes were causing the problem but the lines have not re-appeared so perhaps it is worth a try for you.