Your spline is way too tight and all of that white is giving you problems. Include some of the shot behind the screen, or try just drawing creating a small spline around the corners of the monitor, make sure Perspective is turned on. You are also only tracking 20% of the pixels and more than 80% of the area inside the spline is white with no texture. That leaves you nothing to use for data. Something like this should track just fine:
The track will also go a lot faster if you just track the corners because fewer pixels need to be analyzed.