Block not appearing on Block Layout page
I create a block programmaticaly in Drupal 8, then I went to the Block Layout page, expectiong that my block will apear on the page, at the bottom, in the disable section. This was a behaviour in Drupal 7, but not so in Drupal 8. To see and add your block to the regon, you must click on the 'Place block" button, of the desired region. If you did all your coding corectly you will see your block appearing in the modal, with all other available blocks.