Staff Field not showing the user name

Hi
I have activated the plugin "assign Ticket" and it works fine except that the user will not be showed. For each Staff an empty line will be added to the field. Any idea what I did wrong?

Hello Thomas

If everything properly configured, the system should show username of the staff instead of blank space like that

In this case, could you please submit a support ticket sending us super admin account of your site? I will take a quick look at it to see what's wrong and get it sorted

Regards,

Tuan