In the latest version of Photoshop 21.0.2 and in 21.01 the clone tool and the healing brush is not working as expected. It will copy from one spot to another on the same image, but if two image files are used it is broken. Here is what I found. it is not calculating the copy space properly, If the source and target areas have the same dimensions, then it copies as it should, However as the size of the target area increases, the amount copied decreases, until it does not copy at all. I experimented like this: the source file was 500 X 500 pixels, I copied on to a target area of the same size, perfect. then I tried a target area of 1000 by 1000 and only part of the image would show, it was oddly clipped. then: 1500 by 1500 target area, even less. If I tried to copy a 500-pixel detail from a source image to a large target file that was 2550 pixels by 3300 pixels, nothing would copy. The workaround: Make a blank page the same size as your target area, drag the small source file onto it, flatten, then you can copy from it to your target file. I also found that version 20.0.8 does not have this bug. So I am working from that version for now.