Harmony Advanced - Previous brush stroke disappearing when drawing

Working in Harmony Advanced free trial on windows computer. Sometimes when drawing on a drawing layer the previous brush stroke, or an entire section of the drawing, will disappear. At first I thought it was just the layer overloading for some reason, but it has happened on layers with lots of brush strokes and layers with only 2 or 3, so layer capacity doesn’t seem to be an issue. When I hit undo it undoes the brush stroke and restores lost color, and hitting redo recreates the same issue. Has anyone else experienced this? (Picture

of issue below)