Let's see how to update your Drupal site between 8.x.x minor and patch versions. For example, from 8.1.2 to 8.1.3, or from 8.3.5 to 8.4.0. I hope this will help you.
The approach to custom block caching is different in Drupal 8 from Drupal 7. In Drupal 8, all renderable arrays are cacheable, even those returned by custom block.