Black squares appear when using patch tool

Hi there, I still haven't found an answer to this problem... anytime I use the patch tool not at 100% or 90% I get these black squares on my image and I have to move the image for them to go away. It's really a pain.  I'm using Adobe Photoshop 2020 with an older computer but still this shouldn't happen. Does anyone know how to fix this besides turning off the graphics processor because that doesn't work. Thanks you!