Is there any way to force a custom block in the Custom Block Library to invalidate cache on edit update?
I came across this question in the related questions sidebar on my question that seems to be the same issue with out-of-the-box core blocks:
Block cache not clearing on save?

The accepted answer from @4k4 on that question seems to confirm the issue, but doesn't hook in to the block save to invalidate the cache like I was thinking, but mentions, as one possible workaround, adding this to the theme:

function mytheme_preprocess_block(&amp;$variables) {
  if ($variables['base_plugin_id'] == 'block_content') {
  $renderer = \Drupal::service('renderer');
  $renderer-&gt;addCacheableDependency($variables, $variables['content'}['#block_content']);
  }
}


I don't know if this is the best answer, but it's simple and straightforward and seems to work at the moment, though it's a wonder that this would need to be done at all.  It's probably less of a hack than what I was thinking.