Auth::user() returning NULL

I am facing an issue after I upgraded Laravel 5.2 to 5.6. I am using Valet on mac and I found that after I Auth::login() I could do Auth::user() and fetch the details on the same route where I had called Auth::login. The issue arises when I go to a different route and try to do Auth::user() nothing comes in return.

I also noticed that new sessions are getting created when I go to a new route to do Auth::user().

My kernel looks like this:-

<?php

namespace App\Http;

use Illuminate\Foundation\Http\Kernel as HttpKernel;

class Kernel extends HttpKernel
{
    /**
     * The application's global HTTP middleware stack.
     *
     * These middleware are run during every request to your application.
     *
     * @var array
     */
    protected $middleware = [
        \Illuminate\Foundation\Http\Middleware\CheckForMaintenanceMode::class,
    ];

    /**
     * The application's route middleware groups.
     *
     * @var array
     */
    protected $middlewareGroups = [
        'web' => [
            \App\Http\Middleware\EncryptCookies::class,
            \Illuminate\Cookie\Middleware\AddQueuedCookiesToResponse::class,
            \Illuminate\Session\Middleware\StartSession::class,
            \Illuminate\View\Middleware\ShareErrorsFromSession::class,
            //\App\Http\Middleware\VerifyCsrfToken::class,
            \Illuminate\Routing\Middleware\SubstituteBindings::class,
        ],

        'api' => [
            'throttle:60,1',
            'bindings',
        ],
    ];

    /**
     * The application's route middleware.
     *
     * These middleware may be assigned to groups or used individually.
     *
     * @var array
     */
    protected $routeMiddleware = [
        'auth' => \App\Http\Middleware\Authenticate::class,
        'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,
        'can' => \Illuminate\Foundation\Http\Middleware\Authorize::class,
        'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,
        'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,
        'adminmiddleware'=> \App\Http\Middleware\Adminmiddleware::class,
        'clientmiddleware'=> \App\Http\Middleware\Clientmiddleware::class,
        'adminpermissionmiddleware' => \App\Http\Middleware\AdminPermissionMiddleware::class,
        'checklang'=> \App\Http\Middleware\Checklang::class,
        // 'bindings' => \Illuminate\Routing\Middleware\SubstituteBindings::class,
        'editCategoryUrl'=> \App\Http\Middleware\EditCategoryUrl::class,
    ];
}

My route service provide

<?php

namespace App\Providers;

use Illuminate\Routing\Router;
use Illuminate\Foundation\Support\Providers\RouteServiceProvider as ServiceProvider;

class RouteServiceProvider extends ServiceProvider
{
    /**
     * This namespace is applied to your controller routes.
     *
     * In addition, it is set as the URL generator's root namespace.
     *
     * @var string
     */
    protected $namespace = 'App\Http\Controllers';

    /**
     * Define your route model bindings, pattern filters, etc.
     *
     * @param  \Illuminate\Routing\Router  $router
     * @return void
     */
//    public function boot(Router $router)
//    {
//        //
//
//        parent::boot($router);
//    }

    /**
     * Define the routes for the application.
     *
     * @param  \Illuminate\Routing\Router  $router
     * @return void
     */
    public function map(Router $router)
    {
        $this->mapWebRoutes($router);

        $this->mapApiRoutes($router);

        $this->mapAdminRoutes($router);
    }

    /**
     * Define the "web" routes for the application.
     *
     * These routes all receive session state, CSRF protection, etc.
     *
     * @param  \Illuminate\Routing\Router  $router
     * @return void
     */
    protected function mapWebRoutes(Router $router)
    {
        $router->group([
            'namespace' => $this->namespace, // 'middleware' => 'web',
        ], function ($router) {
            require app_path('Http/routes.php');
        });
    }


    /**
     * added a seperate route for api routes
     * @param  \Illuminate\Routing\Router  $router
     * @return void
     */
    protected function mapApiRoutes(Router $router)
    {
        $router->group([
            'namespace' => $this->namespace, 'middleware' => 'api',
        ], function ($router) {
            require app_path('Http/api-routes.php');
        });
    }


    /**
     * added a seperate route for api routes
     * @param  \Illuminate\Routing\Router  $router
     * @return void
     */
    protected function mapAdminRoutes(Router $router)
    {
        $router->group([
            'namespace' => $this->namespace, 'middleware' => 'web',
        ], function ($router) {
            require app_path('Http/admin-routes.php');
        });
    }
}

My routes where I am checking these

Route::group(['middleware' => 'web'], function()
{   
    // I load the view form
    Route::get('test-view', function(){
        return view('admin.loginTest');
    });

    //I try to login the user here.
    Route::post('login-user', function(Request $request){
        $email = $request->email;
        $password = md5($request->password);
        $admin = App\Admin::where([ ['email', $email], ['password', $password] ])->first();
        if (!is_null($admin)) {
            Auth::login($admin);
            return redirect('/check-auth');
        }
    });

    // I check the user logged in or not here
    Route::get('check-auth', function(){
        echo "<pre>";
        print_r(Auth::user());
        die;
    });

});

My config/auth

<?php

return [

    /*
    |--------------------------------------------------------------------------
    | Authentication Defaults
    |--------------------------------------------------------------------------
    |
    | This option controls the default authentication "guard" and password
    | reset options for your application. You may change these defaults
    | as required, but they're a perfect start for most applications.
    |
    */

    'defaults' => [
        'guard' => 'web',
        'passwords' => 'users',
    ],

    /*
    |--------------------------------------------------------------------------
    | Authentication Guards
    |--------------------------------------------------------------------------
    |
    | Next, you may define every authentication guard for your application.
    | Of course, a great default configuration has been defined for you
    | here which uses session storage and the Eloquent user provider.
    |
    | All authentication drivers have a user provider. This defines how the
    | users are actually retrieved out of your database or other storage
    | mechanisms used by this application to persist your user's data.
    |
    | Supported: "session", "token"
    |
    */

    'guards' => [
        'web' => [
            'driver' => 'session',
            'provider' => 'users',
        ],

        'api' => [
            'driver' => 'token',
            'provider' => 'users',
        ],
    ],

    /*
    |--------------------------------------------------------------------------
    | User Providers
    |--------------------------------------------------------------------------
    |
    | All authentication drivers have a user provider. This defines how the
    | users are actually retrieved out of your database or other storage
    | mechanisms used by this application to persist your user's data.
    |
    | If you have multiple user tables or models you may configure multiple
    | sources which represent each model / table. These sources may then
    | be assigned to any extra authentication guards you have defined.
    |
    | Supported: "database", "eloquent"
    |
    */

    'providers' => [
        'users' => [
            'driver' => 'eloquent',
            'model' => App\Admin::class,
        ],

        // 'users' => [
        //     'driver' => 'database',
        //     'table' => 'admin',
        // ],
    ],

    /*
    |--------------------------------------------------------------------------
    | Resetting Passwords
    |--------------------------------------------------------------------------
    |
    | Here you may set the options for resetting passwords including the view
    | that is your password reset e-mail. You may also set the name of the
    | table that maintains all of the reset tokens for your application.
    |
    | You may specify multiple password reset configurations if you have more
    | than one user table or model in the application and you want to have
    | separate password reset settings based on the specific user types.
    |
    | The expire time is the number of minutes that the reset token should be
    | considered valid. This security feature keeps tokens short-lived so
    | they have less time to be guessed. You may change this as needed.
    |
    */

    'passwords' => [
        'users' => [
            'provider' => 'users',
            'email' => 'auth.emails.password',
            'table' => 'password_resets',
            'expire' => 60,
        ],
    ],

];

I tried to look out and found this link https://github.com/laravel/framework/issues/13000 which I suspect could be the issue but I have tried all of these and still face the issue.

Please assist if anyone has ever faced this issue. Thank you.