Shift command 4 not working

Shift command 4 turns the cursor into a camera and takes a screenshot of the entire screen, instead of turning it into crosshairs and making a selection. All other screenshot shortcuts work as expected.

I haven't had a problem with this until today

Running 10.13.5 on a 2017 13-inch macbook pro.

I have done all this:

Rebooted

Reset PRAM/SMC

Fooled around with keyboard shortcut settings in system preferences

Run first aid in disk utilities

Moved the com.apple.imagecapture plist file to desktop and restarted

Any other suggestions? And, yes, I know I can use Grab. I'd like to get the screenshot shortcut working again.

Thanks so much!