What it appears is the router after the level3 point was down or the connection after it.. Now that it is working, rerun that test and you can find the exact router. In cases like this, I would call your own ISP and let them know your results. They might be able to track them down. Most of the time I query it and I can find out a contact number.
Level3 is fairly large now so I would imagine it is something on their end. Any number of issues could cause this from fiber issues all the way to hardware. Of all the companies they are the most difficult to contact and get anywhere with. We have our fiber running through one of their substations and it took hours to even find someone to help us get access into it.