adf.context.getSecurityContext().getUserName() does not return results for a specific user

We are using standard groovy function "adf.context.getSecurityContext().getUserName()" to set user who approved ticket to a custom field

Below is the code

setAttribute('TicketApproverName_c',adf. context. getSecurityContext(). getUserName())

It does not get set for only one user, any reasons why it would not work?

I checked the user set up like username, resource role etc and everything looks good.