You have idea, project, or custom investment custom attributes you want to show in the roadmap item list view. These fields aren't available to select in the roadmap item list, and you can't create virtual attributes on the roadmap item object for anything but the roadmap object.
Release : All Supported Releases
Here are the steps below on how to add/sync the fields from your idea/projects to roadmap items using the idea example. (The API Attribute ID, Lookup Data Type, and Lookup must all match for both the Investment object and Roadmap Item object)
See supported attributes for synchronization at: Unable to update API Attribute ID in Roadmap Item object