I've been trying to figure out for 3 days why my newest objects weren't showing up in the map editor.
Finally i tried to reset the preview image in the content tool and it showed up. Aperently I forget to choose the persective.
Maybe it's a good idea to auto set to the first perspective if nothign was selected. So the object atleast shows up in the map editor. And when the perspectiv eis wrong this will be obvious for the author. Currently there is no way to discover a missing perspective is causing the object not to show up. There are no errors, nothing.