I see a lot of these points going over land, even where there aren't any big rivers. Maybe this is a plot of the containers rather than the ships?
There are so many edge cases and oddities that the more you look the more you’ll find.
The moral of the story here is that you cannot accept AIS data, or any single data source, to be God’s Truth; you must always skeptical of the data before your eyes, lest you fall victim to “The Analyst’s Fallacy” (believing that the data presented is all the data there is) and create false stories in your mind.
e.g. 8 June 2012 05:00 from western Sahara to English Channel, through Sahara, right the middle of Spain, parts of France.
Another on 9 May 2012 from Southeast Asia, straight through the south of India and right through the middle of Africa to somewhere on the Guinean Gulf in about half a day.
Not sure why this would be the case. Transponder turned off? Data missing for other reasons?
I've never seen a perfectly clean dataset of any significant size. Big datasets have all sorts of weirdness unless there was an extraordinary effort to keep them pristine.