When users attempt to create an issue and leave the Assignee to "Automatic" it returns the following error:
The default assignee does NOT have ASSIGNABLE permission OR Unassigned issues are turned off.
Unassigned Assignees is turned off, which means it should get assigned to the project leader, which is my user account.
If I change the assignee to my user account, the issue is created.
I've re-indexed the project; changed the assignable user to no effect and changed it back (currently granted to the Project lead, Service Desk Team, and Administrators)