Drush cache needs to be cleared.
In order to run a drush cache clear you simply need to run the following command:
drush cc drush
If for whatever reason this command doesn’t work or the cache hasn’t been fully cleared, you can manually remove the contents by using the following:
rm -rf ~/.drush/cache/*
When drush changes take place such as the addition of new drush commands, drush might behave in unexpected ways. A good first step to troubleshooting issues such as these is to run a cache clear on drush itself.