As you can see here, there is random cargo floating in the air on some maps. Sometimes this is cargo that is on a loading deck in another map, for example, if in black river there are wooden planks on the loading deck of the sawmill, there are wooden planks floating in the air in another map. I don't know if this cargo is actually floating there, I haven't seen it, I think it just shows it in the menu but its not actually there, if that makes sense.