Issue: I can no longer see External User License Type under Access Level Setup.
Conditions: External User is a default license type for non-Workfront users to have the ability to VIEW projects/tasks/issues and calendars that are assigned to them via email. The External User can not be removed, nor can a new Access Level be created with this license type. It is a default setting that can only be renamed.
Resolution: As System Administrators under the setup> system> preferences> access> ensure the box, "Collaborate with people without Workfront accounts by using their email address" is checked. If this box is not check, External User will not appear in Access Level Setup.