Simple module to add a custom block with custom twig template, Work alright but then 'Theme Hook Not Found' after cache clear

Hello Everybody!

i just switched to Drupal 8, and I have a weird issue while programming a new custom module
it’s a simple module to add a custom block, and the custom block is themed (so that i can use a twig template)
it’s working great on install and setting up of the block (placing it on the page), it displays great
but when i do a clear cache, my twig template content is gone from displaying, and in the error log it says it cannot find my theme hook used for that block.
but it all works good before a cache clear. If i reinstall it works good until i cache clear.

Here’s the code :

flycloud_blocks.info.yml (at /)

name: FlyCloud Blocks
description: Where all custom blocks are stored
package: FlyCloud Modules
type: module
version: 1.0
core: 8.x

---
PageFooterBlock.php (in /src/Plugin/Block)

namespace Drupalflycloud_blocksPluginBlock;

use DrupalCoreBlockBlockBase;

/**
 * Provides the Page Footer Block.
 *
 * @Block(
 *   id = "page_footer_block",
 *   admin_label = @Translation("Page Footer"),
 * )
 */
class PageFooterBlock extends BlockBase {

  /**
   * {@inheritdoc}
   */
  
  public function build() {
    return array(
	  '#theme' => 'faq',
      '#items' => array(),
    );
  }

}

---
flycloud_blocks.module (at /)

function flycloud_blocks_theme($existing, $type, $theme, $path){
	return array(
		'faq' => array(
		  'variables' => array(
			'items' => array(),
		  )
		)
	);
}

---
faq.html.twig (in /templates/)

<h1>yessss</h1>

Any ideas? … makes me want to go back to Drupal 7

Thank you very much for your help!

Drupal version: 


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