Rails 6 - Yarn Font Packages Not Working On Production

I'm trying to add some font libraries using Yarn, like this one: https://www.npmjs.com/package/fontsource-poppins.

They're working fine in development but not in production.

application.js

require("@rails/ujs").start()
require("turbolinks").start()
require("@rails/activestorage").start()
require("channels")
require("fontsource-dancing-script")
require("fontsource-poppins")

application.css

 @import "fontsource-dancing-script/600.css";
 @import "fontsource-poppins/400.css";
 @import "fontsource-poppins/300.css";
 @import "fontsource-poppins/200.css";
 @import "fontsource-poppins/100.css";

package.json

{
  "name": "xxxx",
  "private": true,
  "dependencies": {
    "@rails/actioncable": "^6.0.0",
    "@rails/actiontext": "^6.0.3-4",
    "@rails/activestorage": "^6.0.0",
    "@rails/ujs": "^6.0.0",
    "@rails/webpacker": "4.3.0",
    "fontsource-dancing-script": "^3.0.5",
    "fontsource-poppins": "^3.0.10",
    "trix": "^1.2.0",
    "turbolinks": "^5.2.0"
  },
  "version": "0.1.0",
  "devDependencies": {
    "webpack-dev-server": "^3.11.0"
  }
}

I'm not getting any errors during deployment, but when I check the sources tab in devtools, I see that the required files are missing.