Thank you Michael.

The hole is about the same width as the view controls toolbar. It has always been on.

Your size questions triggered the following:

The Snaggit13 window, which is minimized as a thin sliver at the top of the screen, is also the size of the "hole".
The hole occurs below the minimized snagit13 window. Sliding snaggit13 horizontally causes the hole to move the same.
Closing Snaggit13 eliminates the "hole" problem!

- Brian

(I'm going to miss snaggit:-) but it can be closed, and reopened when needed.