I'll get a video done, but have discovered:
First - I do have saved Perspectives. Not a problem.
When I dock the Sequence Elements to the Top (above the Timeline), then Undock, that is when it goes blank.
When I re-dock, it comes back.
BUT - if I dock to the left side of the screen and THEN undock, it is all visible. All views and models are visible.
so, it is position dependent for the docking error. Again, this is in 4.1.12. I never noticed in earlier versions because I never did it.