Rating Photos with Keyboard doesn't work. sometimes.

It’s been happening for a while now. Typing the 1 thru 5 numbers on the keyboard to rate photos doesn’t work. Restarting LR CC works. 
It’s frustrating because I just went thru 300 photos and the ratings didn’t stick so I had to start all over again. 
It has happpened before and it’s random. 

Like I said, restarting LR works again…

☹️