Symptoms

When the user clicks on 'Edit', the assignee is set to 'Automatic', even if the issue is already assigned.

For example, an issue is assigned to 'John'. However, when the user clicks on 'Edit' for that issue, the assignee is set to 'Automatic'.

Cause

Currently root cause of the issue is unknown. The issue seems pretty intermittent. 

Resolution

Re-index your JIRA instance. You can do this at your 'Administration' > 'System' > 'Advanced' > 'Indexing' menu. There, select 'Re-index'.