Stretching the main window above a certain limit will make the window flicker when the drawing is moved. Seems to be the product of with x height that is the problem. Attatching one flickering and one non flickering screenshot.
Zoom factor is not affecting the behaivior. My guess is that some buffer is too small (perhaps designed long before there were 4k monitors available).
Made a movie describing the bug: https://youtu.be/nS_urXqS-tQ