Your loaders do not use the "mdrn-loader-structure-back-patch" and "mdrn-loader-structure-front-patch" graphics but it's easy to add in.

All you gotta do is go to entities.lua and add to "structure = {

  back_patch =
  {
    sheet =
    {
      filename = "__loaders-modernized__/graphics/entity/mdrn-loader-structure-back-patch.png",
      priority = "extra-high",
      width = 192,
      height = 192,
      scale = 0.5
    }
  },
  front_patch =
  {
    sheet =
    {
      filename = "__loaders-modernized__/graphics/entity/mdrn-loader-structure-front-patch.png",
      priority = "extra-high",
      width = 192,
      height = 192,
      scale = 0.5
    }
  }

Thanks! It'll be fixed in the next version.