I figured out that the score editor is very unstable. When I open the score editor, and it shows the notes for the region I clicked on, I now know to be sure to only click on the white, lit area of the stave to increase the view to either multiples of the same region, or the full score. If I click on the gray area, then the whole thing goes black and "create a MIDI region" appears, and the score editor will no longer come back. Also, do not ever click on a region when the score editor is open, or the whole thing goes black again.
The score editor is very unstable, and must be opened and closed with care. Once the "create a MIDI region" prompt comes up, it is impossible to get the score editor to open again, unless you open the specific score editor window, but that will not display the full score.