My rendered animation shows a large streak on some of the frames, and not on others. The streak doesn't show in the viewport, only in the final render. Rendered using cycles.
Here is what the Render should look like. It's relatively normal.
Now earlier in the animation, there is a large streak up. (Image cropped for file size issues)
Here's the mug part of the composite.
Here's the shadow part of the composite. (Can't be seen over black background)
Here are the composite nodes used. They are the default for motion tracking. I haven't changed them.