Red line on map?
 

So I opened up my map in the treasure chest and I saw a dashed line going toward Kingshead and it looped back around.. and I went back in the game and it disappeared.. any ideas as to what this could be?

The red dashed line is the path that a Treasure fleet is taking. It will only show on your map if a fleet is sailing at that moment. It's possible a fleet sank as you were noticing it so the line disappeared when you checked your map again.

Aye, many people have clamored about this. I didn't know that until a month or so ago.