When making a mask the selection will intermittenly go in a straight line to the far left of the photo.

Sometimes, when I’m making a new mask (object selection or brush), the selection will go to the far right in a straight line. I am using an iMac M3 26.5.2 and Lightroom Classic 15.41 at the moment, but this problem has persisted through many LR and OS updates. You can see it in the attached screenshot. I was trying to dodge certain areas on the bronze plaque, and the selection went feral! I have contacted Adobe Help, but they didn’t solve the problem.