Autoloading of classes through composer does not work

I have a project structure:

In the index.php I create 2 new objects:

use App\Controllers\Test;
use Xuborx\Cms\App;

new Test();
new App();

My Test.php

<?php

namespace App\Controllers;

class Test
{

}

My App.php

<?php

namespace Xuborx\Cms;

class App {

}

My autoload object in composer.json:

"autoload": {
        "psr-4": {
            "App\\Controllers\\": "app/controllers",
            "Xuborx\\Cms\\": "vendor/xuborx/cms"

        }
    }

Object Test created successfully in the index.php, but when I am creating new App, I have an error:

Fatal error: Uncaught Error: Class 'Xuborx\Cms\App' not found in /home/denis/Coding/xuborx-cms/public/index.php:8 Stack trace: #0 {main} thrown in /home/denis/Coding/xuborx-cms/public/index.php on line 8

Also, when I run composer dump-autoload -o, I get error:

Class Xuborx\Cms\App located in ./vendor/xuborx/cms/core/App.php does not comply with psr-4 autoloading standard. Skipping.

I think, I not correct use autoload in composer.json, but I don't understand my error. Please< talk me about it.

App.php are inside /core directory :

autoload": {
        "psr-4": {
            "App\\Controllers\\": "app/controllers",
            "Xuborx\\Cms\\": "vendor/xuborx/cms/core"

        }
    }