Problem

Custom created user picker field value was empty in the email notification however system field assignee has the value in the email notifications when Email from settings ${fullname} (Jira) was updated to ${fullname} (mycompanyname Jira) under global settings.
Thi will always happen when Email from settings updated to nondefault value ${fullname}(Jira) 

Environment

Jira Cloud

Steps to Reproduce

As a site Admin:

1. Navigate to the Global settings of your instance.
2. Update Email from ${fullname} (Jira)  to ${fullname} (mycompanyname Jira)
3. Create a custom user picker field and assign it to a project.
4. Create an issue and change the custom-created user picker field value.
5. Custom created user picker field value is null in the triggered email notifications

Expected Results

Custom created user picker field value display the updated value in the triggered email notification

Actual Results

Custom created user picker field value is null in the triggered email notification

Workaround

Update Email from settings ${fullname} (mycompanyname Jira) to ${fullname} (Jira) under Global settings.