Hi Max - it's not unusual to get n-gons possibly with some of their points nearby each other in various juncture areas. There it looks like it's the cut through the middle to deal with the interior hole in the top surface that is probably introducing the points you don't want. That's just part of how the mesher works... OBJ format does not have the concept of a polygon with a hole in it, so any n-gons that would have internal holes within a single n-gon like the top face there will get divided which can easily introduce additional boundary points.

- Michael