Creating a Test Execution from a Test Plan with an assignee does not work if the username has been edited

Description
Creating a Test Execution from a Test Plan with an assignee does not work if the username has been edited.

Pre-conditions

1. Have a required field for when creating the issue to open the Jira Create screen.

How to reproduce

1. Create a Test Plan and add 2 Tests assigned to username admin;
2. Go to User Management and change the username admin to admin2;
3. Create a Test Execution inside of a Test Plan;
4. The error appears.

Actual result/Attachments

**An error appears: User 'JIRAUSER10000' does not exist.
See gif attached. 

Expected result

The Test Execution should be created correctly.
Workarounds for this case:
1. delete the assignee field on the Create screen and write it again
2. Remove the required fields. On the internal Xray Create screen, this problem does not occur.

Version

• 4.1.6
• 4.2.11