The magic missile implementation is the standard 5E D&D one if I remember correctly? That doesn't scale like the magic missile of older D&D versions -
https://roll20.net/compendium/dnd5e/Magic%20Missile#contentI think it is working as expected (although the targeting is a bit wonky - you don't need line of effect to targets, only line of sight, but they treat it like an actual projetile, or did, last time I played).
NOTE: you can upcast it though to add more missiles.