The gray concentric circles representing the adjustment brush disappear when mousing over the image but not the toolbar. The brush shows at sizes from about 9 and higher. It inconsistently shows up and disappears between sizes 8 and 9. So, if I have the brush set at 7 for example, as soon as I move the cursor from the toolbar to the image, the cursor completely disappears and I cannot see where I am brushing.
I am using the latest version of Lightroom Classic CC on a 2017 MacBook Pro 13-inch running Mac OSX 10.13.3. The laptop is connected to an LG 5K monitor, which I think may be where the problem lies, but no idea how to fix it.