Running Laravel Elixir as production skips some sass files

I'm running Laravel 5.3 with the basic Elixir setup. My gulpfile.js:

const elixir = require('laravel-elixir');
require('laravel-elixir-vue');

elixir(mix => {
    mix.sass(['app.scss', '**/*.scss'], 'public/assets/css')
        .webpack('app.js');
 });

When running "gulp" or "gulp watch" it compiles nicely, but "gulp --production" treats the mix command like

mix.sass(['app.scss'], 'public/assets/css')
        .webpack('app.js');

ie. the wildcard sass includes are ignored. What to do?

via Chebli Mohamed