You have multiple Users that were imported using AD Import. Some will appear as their "Login name" and others as their "Display name". You want the resources to display as "Display Name" when this field is populated in AD.
Currently, you need to Edit the asset resource in order to make the change in how these Users resources are displayed.
This is already the "Display Name" as one field set to be imported and AD has this field populated for all those Users that are currently displaying just the "Login Name":
ITMS 8.6
This issue has been addressed with the ITMS 8.7 release.