Can't see users when editing assignee in Jira cloud even with permissions

Summary

A user can't see or add another user to the assignee field of work items in Jira Cloud projects.

Diagnosis

Steps from the documentation Jira user can't see or search others in user-picker fields like Assignee have already been followed:

• The affected user has the Browse users and groups global permission

• The user that is supposed to be assigned has the Assignable user permission

Cause

Jira's database is out of sync, or indexing is required. This can be caused when a Jira userbase is particularly large, or has undergone significant additions during a Cloud migration.

Solution

Manually remove and re-add the user to the Jira default group

Removing and re-adding the user triggers a sync manually, which resolves the issue.

1. Navigate to admin.atlassian.com

2. Identify the Jira default group

3. Search for the user under the Users section

4. Remove the user from the default access group 

5. Re-add the user to the default access group

This process will trigger a sync. Within a few minutes, the sync will complete, and the issue should resolve.