Summary

It's not possible to edit the Component Lead and assign it to specific users whose usernames have been renamed before. Below error message is shown:

The user "username" does not exist.

Steps to Reproduce

1. Have a project and some Components. 
2. Have a user and rename it (i.e from John to A).
3. Edit the component lead for a component and set it to the renamed user.
4. Receive a "The user "username" does not exist." message.

Expected Result

Able to assign A as the new Component Lead for the selected component.

Actual Result

Receive a "The user "username" does not exist." error message.

Workaround

Update the component lead using REST API:

curl -D- -u admin_username:admin_password -X PUT --data "{\"leadUserName\": \"<user_name>\"}" -H "Content-Type: application/json" <JIRA_URL>/rest/api/2/component/<component_ID>

<user_name>, <JIRA_URL>, and <component_ID> are to be replaced accordingly
The command is to be run by a JIRA admin and he must authenticate using his admin_username and admin_password

Tips

In order to quickly get <component_ID> via REST API:

1. Access this URL replacing <project_Key> with actual project key:

   <JIRA_URL>/rest/api/2/project/<project_Key>
   

2. Search for component/ and get the ID of the right component:

   /rest/api/2/component/10200","id":"10200","name":"component 1"

   In this example the component with name "component 1" has ID 10200