Why doesn't anything happen when I select a search action from the CiviCRM search results?
The cause was that I had the "Select2" Drupal module installed, which was adding a second Select2 widget to my search actions, breaking them.  

To resolve:


Go to Drupal Configuration menu » User Interface » Select2.
Click the Exclusion Rules tab.
Under Don't load Select2 for specific pages, enter civicrm/* and save your changes.


This should fix your search actions.