Hello! Not sure whats happening here. The bug kicks in randomly after a little while of usage. At that point, moving the mouse cursor seems to drag the glitch around the screen. Nothing I do seem to reset the display until I close down the app and run it again. Captured some video, maybe someone has seen this before?
Aseprite 1.2.21 - Got it via Steam, running it on a mac OSX 10.13, 13 inch MBP.