Doesn’t Work with WP 4.8.3

It works fine.
There must be a different issue on your site.

Not sure if this helps …

I ran into an issue when I tried to hide widgets in individual posts that belong to specified categories (i.e. categories I choose in the widget admin). I fixed it by adding this code to the plugin’s main restrict-widgets.php file, at line 1477:

} elseif (is_single() ) {
  $valid_option = false;
  foreach (get_the_category() as $c) {
    if (isset( $options['category_' . $c->term_id] )) {
      $valid_option = true;
      break;
    }
  }									
}

PS Watch the braces {} to ensure the if..elseif…else statement is properly closed out.