I keep digging up this same information from some obscure sources, so I thought I would post it here. Now if you have not set up XDebug with a project locally, I highly recommend that, but still, nothing beats a good stack trace. In Drupal 7, I would drop this into settings.php to show errors, regardless of the site settings:
The 8th release of the Drupal content management framework.
I've noticed an issue crop up recently where drush seems unable to download new modules, or update existing ones with the drush dl and drush up commands. The issue is that some versions of wget shipped with Redhat Enterprise Linux failed to check SAN names in certificates properly. This article from fastly explains the issue well. Note that Drupal.org hosts its updates server on fastly.
You can see where drush is failing by using the verbose flags