User criteria on the catalog item excludes the current user from viewing the item due to role, department, location, or other attribute restrictions. (high likelihood)
The catalog item is assigned to a category that is not published or visible to the user's current role or portal configuration. (high likelihood)
ACL (Access Control List) rules are blocking read access to the sc_cat_item table or related catalog tables for the user's role. (medium likelihood)
The catalog item's availability is restricted by start/end dates that exclude the current date and time. (medium likelihood)
The catalog item's portal visibility settings exclude the specific Service Portal where the user is browsing. (low likelihood)