LoadConfiguration.php

<?php

namespace App\Bootstrap;

use Illuminate\Config\Repository;
use Illuminate\Contracts\Foundation\Application;
use Roots\Acorn\Bootstrap\LoadConfiguration as RootsLoadConfiguration;

class LoadConfiguration extends RootsLoadConfiguration
{
    /**
     * {@inheritdoc}
     */
    public function bootstrap(Application $app)
    {
        parent::bootstrap($app);

        // When `wp acorn optimize` runs it will create a cached config.php file
        // with pre-determined values at build times. This causes issues with
        // multisite since the config.php file uses get_theme_file_path() which
        // needs to be dynamically evaluated per site.
        // Here we override the cached config by re-evaluating the config files.
        $this->loadConfigurationFiles($app, $app->make('config'));
    }
}

setup.php

<?php

namespace App;

use App\Bootstrap\LoadConfiguration;
use Roots\Acorn\Bootstrap\LoadConfiguration as RootsLoadConfiguration;

add_filter('acorn/bootstrap', function (array $bootstrap) {
    if ($idx = array_search(RootsLoadConfiguration::class, $bootstrap)) {
        $bootstrap[$idx] = LoadConfiguration::class;
    }
    return $bootstrap;
});