Same problem on my setup as well. So i make sure I have a solid black desktop background to make the glitch less visible.
Do you guys see the same issue if you run the loop directly in VLC? OpenLP is using the VLC engine, so i wonder if it has something to do with file caching or something in the VLC engine?
But one thing I've noticed is that video runs more stable if i reduce the screen size with one pixel less than full screen. Has anyone else tried that?