ACF Blocks incompatible with Underscores.me -themes

Hi Elliot!

I can't figure out why ACF Blocks won't render on front-end of Underscores-based themes. I checked code and it worked in Automattics Twenty * -themes, but does not render on any Underscores.me -based themes.

I have crossed out any plugin or hosting incompabilities, and only clue is starting theme.

Blocks render correctly on Gutenberg-editor, but in front-end they stay as HTML-comments. Block has only one text-field 'title'. I have also copied example codes on ACF Blocks home page but result is same: backend works fine but frontend won't render.

MY CODE IN FUNCTIONS.PHP

// ACF BLOCK CATEGORY
  add_filter( 'block_categories', 'company_block_category', 10, 2);
  function company_block_category( $categories, $post ) {
    return array_merge(
      array( array(
        'slug' => 'company',
        'title' => __( 'company' )
      ) ),
      $categories
    );
  }

  // ACF BLOCKS
  add_action('acf/init', 'register_acf_blocks');
  function register_acf_blocks() {

    // Read More
    acf_register_block_type( array(
        'name'              => 'read-more',
        'title'             => __('Read More'),
        'description'       => __('Read More -block.'),
        'render_template'   => 'acf/blocks/readmore.php',
        'category'          => 'company',
        'icon'              => 'welcome-add-page',
        'keywords'          => array( 'readmore' ),
    ) );
  }

ACF/BLOCKS/READMORE.PHP:

<div>
  <h2><?php echo get_field('title'); ?></h2>
</div>

PAGE SOURCE CODE ON FRONT END:

<!-- wp:acf/read-more {
    "id": "block_5d179c44ebd42",
    "name": "acf\/read-more",
    "data": {
        "otsikko": "",
        "_otsikko": "field_5d08c12a95e74",
    },
    "align": "",
    "mode": "preview"
} /-->

I can't get any errors anywhere and not a single mention about this anywhere in internet. Could you help me out with this one?

Start with the ACF block registration in functions.php and the template at acf/blocks/readmore.php, then compare the saved block markup in the page source with the block's configured field name. Reproduce the frontend behavior using an Underscores-based theme and check whether the block template is reached; done means the block renders its title on the frontend.