Screenshot App (NOT keyboard command, application)

Since I've upgraded to Mojave, when I use the screenshot app to capture a section of my screen, it will take the first screen shot, but then the screen stays dark except for the area where I took the screenshot.

Can't force quit because it doesn't show as one of the applications.

Using the keyboard commands doesn't affect it. In fact, using cmd+Shift+5 I can capture the area of my previous capture.

The only solution I have found is a reboot.

Any suggestions?