I'm using LR Classic CC 7.2 release on a mac pro with 10.13.3. I just noticed that on images when I already have a graduated filter adjustment, I can't paint correctly with the adjustment brush. After I create a new adjustment brush pin and start painting, the area painted grows to about about a third of the image, regardless of how little or much I paint, no matter the brush settings. If I remove the graduated filter, then I can paint with the adjustment brush with no issues. Also, this problem only seems to happen when I have a graduated filter in the same area as the pinned area with the adjustment brush; if I have a graduated filter, say for the sky, and I add an adjustment brush point somewhere below, all is fine.
I've made a screen movie to illustrate the problem: