If Drupal's cron fails then it will be in a broken state that will give you the following error if you attempt to run it again:
Attempting to re-run cron while it is already running
To recover from this error you need to delete the 'cron' record from the semaphore table.
DELETE FROM semaphore WHERE name='cron';
Run this via Drush using the following command.
drush sql:query "DELETE FROM semaphore WHERE name='cron';"