3D Edit view: Clicking on the title bar of the edit view dialog blanks out the view until you move or resize it.
Same thing happens if you click on the title bar of the Design Studio.
Note that it has to be a quick click.
Sometimes, any interaction with design studio does the same, such as clicking on the navigator. This isn't reliable like clicking on the title bar, but when it starts happening it usually keeps happening until you resize the edit view a few times. I haven't yet figured out how to make this start happening reliably, but it does happen often enough to be annoying.
Note that there is always a flicker on 3D edit view when you move focus from it to Design Studio, so it seems it always blanks it, but only sometimes it doesn't manage to restore it.
Opening a new document that should show 3D edit view, such as imported component, also blanks out the edit view reliably.