Changed randomness to be passed as a variable.
$("#grid").mason({
  itemSelector: ".box",
  ratio: 1.5,
  sizes: [
   [1,1],
   [1,2],
   [2,1],
   [2,2],
  ],
  columns: [
   [0,480,1],
   [480,780,2],
   [780,1080,3],

  ],
  filler: {
   itemSelector: '.fillerBox',
   filler_class: 'custom_filler'
  },
  randomSizes:false,
  randomFillers:false,

  layout: 'fluid',
  gutter: 5
 },function(){
  console.log("COMPLETE!")
 });