Programmatically creating mulitple blocks without creating seperate .php files for them

Question

EDIT: The code below works - there was a problem with my local machine - read more at the end for why it did not work

I want to create multiple blocks that don't need custom setttings from the interface and get their content from a custom function based on their name.

So basically I a need a bunch of blocks with names in order to be able to be placed in regions from the UI.

I tried this tutorial but I realize that its from early 2014 and things might have changed so I ended up following the the 1st solution to this question which seems newer.

modules/mymodule/src/Plugin/Block/YourBlock.php

<?php

namespace Drupal\mymodule\Plugin\Block;
use Drupal\Core\Block\BlockBase;

/**
 * Display all instances for 'YourBlock' block plugin.
 *
 * @Block(
 *   id = "mymodule_block",
 *   admin_label = @Translation("Your block"),
 *   category = @Translation("Your block"),
 *   deriver = "Drupal\mymodule\Plugin\Derivative\YourBlock"
 * )
 */

class YourBlock extends BlockBase {
  /**
   * Build the content for mymodule block.
   */
  public function build() {
    $block_id = $this->getDerivativeId();
    return array(
      '#markup' => $block_id,
    );
  }
}

modules/mymodule/src/Plugin/Derivative/YourBlock.php

<?php
namespace Drupal\mymodule\Plugin\Derivative;
use Drupal\Component\Plugin\Derivative\DeriverBase;

class YourBlock extends DeriverBase {
    public function getDerivativeDefinitions($base_plugin_definition) {
        $myblocks = array(
            'mymodule_block_1' => t('My Module: Block 1'),
            'mymodule_block_2' => t('My Module: Block 2'),
        );

        foreach ($myblocks as $block_id => $block_label) {
            $this->derivatives[$block_id] = $base_plugin_definition;
            $this->derivatives[$block_id]['admin_label'] = 
                t('Title: @name content type: @ctype ', array('@name' => $block_label, '@ctype' => "My Module"));
        }

        return $this->derivatives;
    }
}

above is the complete code I have tried

I have done drush cache-rebuild but the 2 blocks don't appear when I press "place blocks" in admin/structure/block

What am I doing wrong ?

EDIT: Found a solution it turns out that enabling this module on a different system the blocks where discovered so there was nothing wrong with the code

The setup that had a problem was with php 5.5.9 and mysql 5.5 and the system that was working well had php7.1 and mysql 5.7 so this might be the case