Photoshop CC 2019: Burn tool creates a rectangular around the brushed area
I am using adobe photoshop CC 2019 with a 5K IMac running OS 10.14.3 Mojave. When I use the burn tool I get a rectangular light or dark area in the image, which goes away when I zoom the screen. I turned off using the graphics processor in Photoshop Preferences, and it doesn’t happen. I don’t want to turn iff the graphics processor. What should I do?