I was editing a photo in Photoshop 21.0.1 using the "Select Color Range" tool, the "Rectangular Selection" tool, and the "Polygon Lasso" tool to select / isolate an irregular area that I wanted to adjust. While refining the selection created by the "Select Color Range" tool several instances of an artifact that looked a lot like a boot appeared at various locations in the image and outside the area that had been selected. I tried to remove these artifacts by using the "Rectangular Selection" tool set to remove or "-" the area marked. That did not remove them. Later I tried to remove small portions of each artifact which did work if I used 4 or 5 selections to do the removal. I have managed to get the selection artifacts out of my selection. I'm thinking that there may be some sort of memory usage conflict causing this problem. Most of the artifacts appear in the area above the light colored sky in the uploaded image. System is Windows 10 Home Premium with all updates installed.