Having a similar issue. Just spun up a new v4.0.5 CMS server to replace our v3 one, selected the standard “1080p HD Landscape” resolution, and the no matter if I choose Fill, Cover, or Contain in scaling, scaling doesn’t work and the media gets cut off on the right and bottom. Used the “Make this full screen” button under positioning just to ensure it was in fact full screen. It happens on previews as well as multiple players. It’s like some other resolution setting is overriding the scaling.
I solved my issue, or at least have a work-around (unsure if this is by design). What I was doing to get the wrong scaling was just dragging the widget/image/pdf from the list over to the canvas as I did in version 3. I worked around this now by dragging a playlist widget to the canvas, making that full-screen, and then adding the other widgets/images/pdfs to the playlist. Then the scaling worked as expected.
Perhaps if you put a playlist first, then add the clock to the playlist?