When I am painting brushstrokes, strange grid like artifacts will appear, making the shading cut off against a straight line. The even bigger issue is these artifacts won't go away after I hit Edit>Undo or close the program. I have to keep manually blending them back in the artwork. I'm not sure what I can do to fix this. I took a screenshot to show what I'm talking about. Does anyone have any advice? I really want to like this program, but I just keep having to deal with more and more issues and it's starting to feel not worth it.
Yep ipetcats is right, if we can get an idea of which brush/settings you are using we can find a setting to improve this and/or tune out the noise. I think you are using a brush with 'stroke attributes', which could be using a 'composite method' that produces artifacts...