Looks like the lower portion of my LCD is trying to readjust its height.
This doesn't show up if I record the screen. It seems to only appear when displaying certain kinds of graphics... like the dark UIs of Blender and Adobe Illustrator. It also shows up if I play back a video of these troublesome GUIs in fullscreen!
What could be causing this?
EDIT: Fixed by moving the image up when the problem occurs.