The best course of action is to restore the project, then the sub-tasks. This is because sub-tasks cannot exist without their parent issues, and parent issues cannot exist without their project. Therefore, restoring the project first will ensure that the parent issues are also restored, and then restoring the sub-tasks will re-attach them to their parent issues. Restoring the parent issues only will not restore the sub-tasks, as they are still archived. Restoring the project only will not restore the sub-tasks, as they need to be restored separately. Restoring the parent issues, then the sub-tasks will not work, as the parent issues cannot be restored without their project. Restoring the project, then the parent issues is unnecessary, as the parent issues are already restored with the project. References: [Restoring an archived issue], [Managing Jira Projects Data Center and Server: Certification Bundle]