Chapters 4 & 6 can alternative between eachother. At the end of Chapter 3 you are given the choice to explore the seashore or volcano. If you chose to explore the Volcano, Battle in the Tropics would be Chapter 6 instead.
While this game is available on both Switch & 3DS, the 3DS version imo is vastly superior in presentation and play. As the game was originally designed for the 3DS and ported to the Switch, I think the Switch version is overly busy and the more top down perspective of the touch screen makes the game easier to play. Not many people will cover the 3DS version, so enjoy! I will not be focusing on S Ranks and 3 Stars on every level.