Error: License assignment for <user> SKU: <guid> assigned indirectly does not exist  (4378221)

When attempting to assign users to an Azure Active Directory group, the AADGroup update job fails with the following error:

License assignment for <user> SKU: <guid> assigned indirectly does not exist 

Navigate to the following location and clear out any outstanding AADGroupHasSubSku objects associated to the affected group.

1. Login to Manager with an applicable account
2. Load the Azure Active Directory menu
3. Expand Target system synchronization: Azure Active Directory
4. Click on AADGroupHasSubSku
5. Click on an outstanding AADGRoupHasSubSku object and select the delete button to remove the object