Banner shows page titles as "Access Denied" due to a block cache

Adding a pre_process function to the theme should fix this.

function <THEMENAME>_preprocess_block(&$variables) {

  if ($variables['configuration']['label'] && $variables['configuration']['label'] == 'Banner') {
    $variables['#cache']['contexts'][] = 'user';
  if ($variables['base_plugin_id'] != 'block_content') {
    return;
  }

  /** @var \Drupal\node\Entity\Node $node */
  $node = \Drupal::routeMatch()->getParameter('node');

  $block = $variables['elements']['content']['#block_content'];

  // If the node is not loaded, adjust the cache max-age of the banner block to -1.
  if ($block && $block->bundle() == 'civictheme_banner' && !$node) {
    $variables['#cache']['max-age'] = 0;
  }
}

Clarifying my above suggestion:

/**
 * Preprocess block function to add additional cache context on Banner block.
 */
function <THEMENAME>_preprocess_block(&$variables) {
  if ($variables['base_plugin_id'] != 'block_content') {
    return;
  }

  $node = \Drupal::routeMatch()->getParameter('node');
  $block = $variables['elements']['content']['#block_content'];

  // If the node is not loaded, adjust the cache max-age of the banner block to -1.
  if ($block && $block->bundle() == 'civictheme_banner' && !$node) {
    $variables['#cache']['max-age'] = 0;
  }
}