One thing that puzzles me - there are thousands of satellites 24/7, CIA has their own, NSA has their own, Navy, Air Force and so on. And all other neighbors around that incident site should be monitoring everything possible. On a very strategically important pipeline for whole continent.

Yet nobody saw anything, there are no past records going few hours back of some ship sailing to those spots? I mean US can spot very shallow speed boats of cocaine smugglers for a long time, so they use submarines from what I gathered.

One explanation would be that submarine, but - if I would be doing marine defense, I would be pinging / doing some other equivalent of radar checks very frequently. But maybe this is really difficult to do due ie shape of sea bottom, reach of such pings, animal protections, just pure costs etc.