Laravel 5.6: Auth::check() fails directly after successful Auth::login

I am using version 5.6 of Laravel.

I try to manually write a login controller which on success leads to the dashboard and on fail back to the login.

The problem is when i try to login the MainController allways redirects back to the login. So i checked if the user got logged in properly in the LoginController by checking if Auth::check works afer logging in and found out that it fails which makes it seem like for some reason the user doesn't get logged in properly even though i don't get any error messages.

I searched for hours and tried many things to fix this issue but with no success. So i hope someone can give me a pointer to how to solve this problem.

My setup looks like this:

web.php

<?php
    Route::get('/', 'MainController')->name('dashboard');
    Route::get('/login', 'LoginController')->name('login');
    Route::post('/login/authenticate', 'LoginController@authenticate')->name('authenticate');

MainController.php

<?php
    namespace App\Http\Controllers;

    use App\User;
    use App\Http\Controllers\Controller;

    class MainController extends Controller
    {
        public function __construct()
        {
            $this->middleware('auth');
        }

        public function __invoke()
        {
            return view('maintenance');
        }
    }

LoginController

<?php
    namespace App\Http\Controllers;

    use Illuminate\Http\Request;
    use Illuminate\Support\Facades\Auth;
    use App\User;

    class LoginController extends Controller
    {
        $user = User::where('userid', $request->input('username'))
            ->where('user_pass', $request->input('password'))
            ->where('state', 0)
            ->first();

            if($user) {
                Auth::login($user);
                if (Auth::check()) {
                    dd('Auth::check() failed');
                }

                //return redirect()->route('dashboard');
            } else {
                return redirect()->back()->withInput();
            }
        }
    }

User.php

<?php
    namespace App;

    use Illuminate\Notifications\Notifiable;
    use Illuminate\Foundation\Auth\User as Authenticatable;

    class User extends Authenticatable
    {
        use Notifiable;
        protected $primaryKey = 'account_id';
        protected $table = 'login';
        public $timestamps = false;
    }

via Chebli Mohamed