Laravel 5: cookie set by custom Middleware not readable in Controller

I created a website with Laravel 5. In order to keep track of users that were referred to by some other website I use the following middleware that recognizes the referral by a request parameter and sets a cookie.

<?php

namespace App\Http\Middleware;

use Closure;

class AffiliateTrackingMiddleware {

    public static $trackingCookieName = "refId";
    public static $trackingURLParameter = "refId";

    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next) {
        $response = $next($request);

        if ($request->has(\App\Http\Middleware\AffiliateTrackingMiddleware::$trackingURLParameter)) {

            return $response->withCookie(cookie()->forever(\App\Http\Middleware\AffiliateTrackingMiddleware::$trackingCookieName, $request->get(\App\Http\Middleware\AffiliateTrackingMiddleware::$trackingURLParameter)));
        }

        return $response;
    }
}

In my controller I would like to retrieve the value of the cookie. I implemented the following function for that. For the case that there is no cookie available I also check if there is a request parameter set to identify the referrer.

protected function getAffiliateId($request = null) {

    $affiliateCookieValue = Cookie::get(\App\Http\Middleware\AffiliateTrackingMiddleware::$trackingCookieName);

    if (!empty($affiliateCookieValue)) {
        return $affiliateCookieValue;
    } else {
        if ($request !== null) {
            if (!empty($request->get(\App\Http\Middleware\AffiliateTrackingMiddleware::$trackingURLParameter))) {
                $affiliateRequestValue = $request->get(\App\Http\Middleware\AffiliateTrackingMiddleware::$trackingURLParameter);
                return $affiliateRequestValue;
            } else {
                $affiliateCookieValue = $request->cookie(\App\Http\Middleware\AffiliateTrackingMiddleware::$trackingCookieName);
                return $affiliateCookieValue;
            }
        } else {
            return "";
        }
    }
}

The strange thing now is that within the constructor of my controller I am able to retrieve the correct affiliate id by cookie. However, when I call the function getAffiliateId from within another function of my controller the cookie value remains empty.

Why is it not possible for me to retrieve the cookie value set up in the middleware from any function in my controller?

In my browser I can also see the cookie.

Added: The code of the Http/Kernel.php

<?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,
        \Illuminate\Foundation\Http\Middleware\ValidatePostSize::class,
        \App\Http\Middleware\TrimStrings::class,
        \Illuminate\Foundation\Http\Middleware\ConvertEmptyStringsToNull::class,
        \App\Http\Middleware\AfterMiddleware::class,
        \App\Http\Middleware\AffiliateTrackingMiddleware::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\Session\Middleware\AuthenticateSession::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' => \Illuminate\Auth\Middleware\Authenticate::class,
        'auth.basic' => \Illuminate\Auth\Middleware\AuthenticateWithBasicAuth::class,
        'bindings' => \Illuminate\Routing\Middleware\SubstituteBindings::class,
        'can' => \Illuminate\Auth\Middleware\Authorize::class,
        'guest' => \App\Http\Middleware\RedirectIfAuthenticated::class,
        'throttle' => \Illuminate\Routing\Middleware\ThrottleRequests::class,
    ];
}

Since you want to use your middleware inside of your web middleware, append your middleware at the end of web group middleware, like so:

'web' => [
    ...
    \App\Http\Middleware\AffiliateTrackingMiddleware::class,
]

Also make sure that your cookies are not empty when the request hits your middleware