Media File in Layout Design, but not Timeline view

Several times, when I remove a media file from a Layout (almost always they are files that were initially uploaded by another person), it still shows up in the Layout Design and Preview, and is still displaying on the digital display. Why might this be happening, and is there a way to remove these files from the display?

Did you just unassign it from your layout or completely deleted the media files from CMS library? (not retired, but fully deleted).

Retired files can still be displayed on the layouts.

If you completely unassign and then delete a media file from the CMS library, then it will no longer be on a layout.
If you just unassign the media from the layout then it will no longer be on a layout.

After media file is no longer on the layout, then it should not be displayed on the signage player - collection interval / layout’s duration may delay this change on the player.