Build not working but rendering HTML

[jmtalarn]

An app using the elm-starter project, https://jmtalarn.github.io/30-days-of-elm/, is working fine while in development I use the npm run start command (aka "node ./src-elm-starter/elm-starter start")
But if I build it in order to be deployed in somewhere static content servant, like it could be github pages, the built is not working. Functionality is not there but no errors in console. Although, the pages are there as the HTML was generated and if you click on links or change the URL to one expected it loads it.

Not just when it is on github pages, also if locally I create the build and then run a static server on the build folder or run the npm run serverBuild (aka "node ./src-elm-starter/elm-starter serverBuild")

Additional Info. Javascript generated file elm-0.0.14-whatever.min.js on elm-stuff/elm-starter-files/build path is filled with an explicit undefined text. Just the word undefined inside the javascript file.