Drupal 8 custom module not showing up in block layout

I have a custom block module for Drupal 8. It is working on my localhost version of drupal (version 8.7.8). When I upload it to the web server (Version 8.7.11), I can enable the module, but it doesn't show up when I try to place the block on the block layout page. I don't have much control of the web server - files are uploaded via a git repository, but other modules I've added work without issues.

My module is just 2 files:

modules/custom/ischool_section_title_level_two/ischool_section_title_level_two.info.yml

name: iSchool Section Title Level Two
description: Provides a block that shows the Level Two title, or Level One if there is no Level Two.
core: 8.x
package: Custom
dependencies:
  - block
type: module

modules/custom/ischool_section_title_level_two/src/plugin/block/iSchoolSectionTitlelevel_two.php

<?php

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

/**
 * Provides a block that shows the Level Two section title, or Level One title if there is no level Two
 *
 * @Block(
 *   id = "ischool_section_title_level_two",
 *   admin_label = @Translation("iSchool Section Title Level Two"),
 *   category = @Translation("Custom"),
 *   context_definitions = {
 *     "node" = @ContextDefinition("entity:node", label = @Translation("Node"))
 *   }
 * )
 */


//code adapted from http://hussainweb.me/an-easier-way-to-get-the-current-node-in-a-block-plugin-in-drupal-8/
//and https://design.briarmoon.ca/tutorials/drupal-8/getting-the-parent-node-of-a-drupal-8-node
class iSchoolSectionTitlelevel_two extends BlockBase {

  public function build() {
    $node = $this->getContextValue('node');
    if (empty($node))  {   
      return [
        '#markup' => "",
      ];
    }

    $L1_Title = $node->getTitle();
    $L2_Title = $node->getTitle();
    $currentNode = $node;

    while (true) {
      $parent_node = $this->getParentNode($currentNode);
      if (empty($parent_node)){
      break;
    }
      $L2_Title = $L1_Title;
      $L1_Title = $parent_node->getTitle();

      $currentNode = $parent_node;
   }

    return [
      '#markup' => $L2_Title,
    ];
  }

  private function getParentNode($node){


    if (empty($node)) return null;
    $menu_link_manager = \Drupal::service('plugin.manager.menu.link');
    $links = $menu_link_manager->loadLinksByRoute('entity.node.canonical', ['node' => $node->id()]);

    // Because loadLinksByRoute() returns an array keyed by a complex id
    // it is simplest to just get the first result by using array_pop().
    /** @var \Drupal\Core\Menu\MenuLinkInterface $link */
    $link = array_pop($links);
    if (empty($link)) return null;



    /** @var \Drupal\Core\Menu\MenuLinkInterface $parent */
     if ($link->getParent() && $parent = $menu_link_manager->createInstance($link->getParent())) {
        if (!method_exists($parent, "getUrlObject")) return null;
        $urlObj = $parent->getUrlObject();
        if (is_null($urlObj)) return null;
        if (!method_exists($urlObj, "getRouteParameters")) return null;
        $route = $urlObj->getRouteParameters();
        if (empty($route)) return null;
        if (!isset($route['node'])) return null;
        $parent_node = \Drupal::entityManager()->getStorage('node')->load($route['node']);
        return $parent_node;
     }
     else return null;
  }

  // cache this block for a definite time.
  public function getCacheMaxAge() {
    return 43200;
  }



}