Lightroom 6 glitch

This is Len.  I am a professional photographer – using Lightroom forever - I am using Lightroom 6 on an iMac. Yesterday, a problem / glitch happened.  In the Develop mode, when I clicked on the “Adjustment Brush,” and then wanted to apply that to an image – after I activated the “Adjustment Brush,” - when I then clicked on the spot on the image, there was no circular icon on the image to show me where that layer would be.  In other words – I could not see or locate the circular icon for that layer.  The layer actually worked – but the icon is missing – and therefore it is useless.  This held true with old files – as well - where I knew there were layers.  When I clicked on the “Adjustment Brush,” icon – there were no circles on the image to show me where the layers were located. 

I tried this on my laptop – and the icon for the adjustment brush worked just fine – so it is only happening on my iMac.  And the other 5 icons to click in that section  - like “Spot Removal” work perfectly on the iMac – so it is only the “Adjustment Brush” that is not showing me the location of the adjustment.

I did try restarting the computer – that did not work.

Any help would be welcome.  Thank you.