All requests landing at GET /

Can you share some parts of your code? Based on the current information I can't really make anything of it. It can be anything at this point. A bad middleware, a catch all route and so on.

Also, did you check all the laravel upgrade guides as well? Not just the Lumen once.

This is my bootstrap/app.php

<?php

require_once __DIR__.'/../vendor/autoload.php';

try {
    (new Laravel\Lumen\Bootstrap\LoadEnvironmentVariables(
        dirname(__DIR__)
    ))->bootstrap();
} catch (Dotenv\Exception\InvalidPathException $e) {
    //
}

/*
|--------------------------------------------------------------------------
| Create The Application
|--------------------------------------------------------------------------
|
| Here we will load the environment and create the application instance
| that serves as the central piece of this framework. We'll use this
| application as an "IoC" container and router for this framework.
|
*/

$app = new Laravel\Lumen\Application(
    realpath(__DIR__.'/../')
);

$app->withFacades(true, [
    'Superbalist\LaravelPrometheusExporter\PrometheusFacade' => 'Prometheus',
]);

$app->withEloquent();

$app->configure('credentials');
$app->configure('prometheus');
$app->configure('operator');
/*
|--------------------------------------------------------------------------
| Register Container Bindings
|--------------------------------------------------------------------------
|
| Now we will register a few bindings in the service container. We will
| register the exception handler and the console kernel. You may add
| your own bindings here if you like or you can make another file.
|
*/


$app->singleton(
    Illuminate\Contracts\Debug\ExceptionHandler::class,
    App\Exceptions\Handler::class
);

$app->singleton(
    Illuminate\Contracts\Console\Kernel::class,
    App\Console\Kernel::class
);

/*
|--------------------------------------------------------------------------
| Register Middleware
|--------------------------------------------------------------------------
|
| Next, we will register the middleware with the application. These can
| be global middleware that run before and after each request into a
| route or middleware that'll be assigned to some specific routes.
|
*/

 $app->middleware([
   // App\Http\Middleware\ExampleMiddleware::class
   // \App\Http\Middleware\Cors::class,
     \App\Http\Middleware\ProcessEssentialHeaders::class,
   \App\Http\Middleware\PrometheusLogging::class,
   \App\Http\Middleware\LogAfterRequest::class
]);

 $app->routeMiddleware([
//     'auth' => App\Http\Middleware\Authenticate::class,
     'cors' => \App\Http\Middleware\Cors::class,
     'authorize' => \App\Http\Middleware\Authorize::class,
     'prometheus' => \App\Http\Middleware\PrometheusLogging::class
 ]);

/*
|--------------------------------------------------------------------------
| Register Service Providers
|--------------------------------------------------------------------------
|
| Here we will register all of the application's service providers which
| are used to bind services into the container. Service providers are
| totally optional, so you are not required to uncomment this line.
|
*/

$app->register(App\Providers\AppServiceProvider::class);
// $app->register(App\Providers\AuthServiceProvider::class);
// $app->register(App\Providers\EventServiceProvider::class);
$app->register(Illuminate\Redis\RedisServiceProvider::class);
$app->register(App\Providers\PrometheusServiceProvider::class);

/*
|--------------------------------------------------------------------------
| Load The Application Routes
|--------------------------------------------------------------------------
|
| Next we will include the routes file so that they can all be added to
| the application. This will provide all of the URLs the application
| can respond to, as well as the controllers that may handle them.
|
*/

// $app->middleware([
//     \App\Http\Middleware\PrometheusLogging::class
//  ]);

// $app->group(['namespace' => 'App\Http\Controllers\V3', 'prefix' => 'api/v3', 'middleware' => 'prometheus'], function ($app) {
$app->router->group(['namespace' => 'App\Http\Controllers\V3', 'prefix' => 'api/v3'], function ($router) {
    require __DIR__.'/../app/Http/Routes/V3Route.php';
});

$app->router->get("/metrics", [ 'uses' => '\Superbalist\LaravelPrometheusExporter\MetricsController@getMetrics']);
// $app->get("/metrics", ['middleware'=>["prometheus"], 'uses' => '\Superbalist\LaravelPrometheusExporter\MetricsController@getMetrics']);


return $app;

I am getting the request as GET / on the very first middleware so middleware is not responsible. I have also seen Laravel upgrade guide, nothing there seems to relate. Also theres no catchall route since I can see that the request is coming as "/" in the first middleware.

I don't see anything strange. Is there maybe anything weird in routes file itself?