Can't manage to install the development version: 503 Service Unavailable

I am trying to get the latest GIT changes so I can test them and this is how I change from beta to the dev version:

1. I run composer create-project flarum/flarum forum/ --stability=dev
2. In composer.json I change version to "dev-master as 0.1.0-beta.4" for core and extensions
3. Run cd forum and ( cd vendor/flarum/core && ./scripts/compile.sh )
4. Then I compile every extension with a command like this:
   
   

   for extension in akismet approval auth-facebook auth-github auth-twitter bbcode emoji english flags likes lock markdown mentions pusher sticky subscriptions suspend tags; do
       cd extensions/flarum-$extension
       bash scripts/compile.sh
       cd ../../
   done

5. I install vagrant box and create database
6. Open flarum.dev and see installer
7. Input all the required data and click on the button. After installation I get 503 Service Unavailable error

What am I doing wrong? What I see is that all tables are empty after installation. Shouldn't there be some settings or basic data stored in them?
Also, are there any logs or some ways to display the real error behind this?

Additional Info
So, the error is triggered from file /vendor/flarum/core/src/Forum/Server.php at line 51.

if (! $app->isInstalled()) {
        $app->register('Flarum\Install\InstallServiceProvider');

        $pipe->pipe($path, $app->make('Flarum\Http\Middleware\StartSession'));
        $pipe->pipe($path, $app->make('Flarum\Http\Middleware\DispatchRoute', ['routes' => $app->make('flarum.install.routes')]));
        $pipe->pipe($path, new HandleErrors($errorDir, true));
    } elseif ($app->isUpToDate() && ! $app->isDownForMaintenance()) {
        $pipe->pipe($path, $app->make('Flarum\Http\Middleware\ParseJsonBody'));
        $pipe->pipe($path, $app->make('Flarum\Http\Middleware\StartSession'));
        $pipe->pipe($path, $app->make('Flarum\Http\Middleware\RememberFromCookie'));
        $pipe->pipe($path, $app->make('Flarum\Http\Middleware\AuthenticateWithSession'));
        $pipe->pipe($path, $app->make('Flarum\Http\Middleware\SetLocale'));

        event(new ConfigureMiddleware($pipe, $path, $this));

        $pipe->pipe($path, $app->make('Flarum\Http\Middleware\DispatchRoute', ['routes' => $app->make('flarum.forum.routes')]));
        $pipe->pipe($path, new HandleErrors($errorDir, $app->inDebugMode()));
    } else {
        // Here is where the error response is generated
        $pipe->pipe($path, function () use ($errorDir) {
            return new HtmlResponse(file_get_contents($errorDir.'/503.html', 503));
        });
    }

Like I said, after the installation I can see that the tables are created and the config.php file, too. The only problem is that $app->isUpToDate() returns false

If I go further, in vendor/flarum/core/src/Foundation/Application.php, at line 113 we have isUpToDate(), where $settings->get('version') returns null