If custom status codes were used in an older build of Service Catalog (such as 12.6 or 12.7) and were then imported into a newly upgraded or fresh install of 12.8 service catalog, the request status section will appear blank. The issue will progress through the different statuses but nothing will be displayed in the UI and attempting to perform an action on a request will yield a blank dropdown.
Status codes are stored in the %USM_HOME%\view\webapps\usm\locale\icusen\request\requestshared.xml file as before but the file itself has changed a bit from older versions, where simply replacing the file (as was the go-to solution in the past when implementing existing customizations) will no longer work.
The recommended method is to incorporate said custom status codes & values from previous builds of catalog, to the 12.8 out of the box file and a create a copy of it in the %USM_HOME%\filestore\custom directory. Recycling services afterwards will allow for the codes to display as needed.