My description is similar to this - Properties box windowing bug - Oracle Forums - except I could get some Properties but not the one I wanted - for Entity.
When I read the post I thought “if the window is open somewhere else” then using <alt><space> should maybe possibly open up the window menu and let me move the hidden screen to a visible screen.
After selecting an Entity and choosing Properties I then selected <alt><space> and the window menu opened on my laptop screen and I selected move. I then hit the <left> ← button and kept it down for a while and, hey-presto, the window eventually appeared on my laptop screen. I can now view the properties of the Entities.