Lr Classic CC Adjustment Brush Size no longer visible, bracket keys don't work

I am using latest LR Classic CC on an iMac with latest OS. 

After using the program for a while the left/right bracket keys no longer work to change the brush size, and the slider for size adjustment in the panel no longer shows the size as you slide it.   The size slider keeps resetting itself to the very left-hand side of slider line after you move it to the right.  When you start painting, the brush shows up as you paint, but no way to know what size it will be or to change it via the bracket or the panel.

When you move the Size slider in the panel, the cursor (which should remain a cursor as you slide the control) changes into what I'd describe as a vertical line with a minus sign on the left and a plus sign on the right.

If I quit LR and restart it, the brush works again for a while, until it doesn't.

Any thoughts on what's going on?