If you have large perspective changes when you track, it may be that your surface is going behind the camera in Mocha and corrupting the data.
In Mocha, problem splines can occur when the tracking data has become so skewed it goes off or “behind” camera; the keyframes the tracking data generates can throw the shape information out of order. You may need to re-track the shape using only translation, scale, rotation, and shear instead of perspective. This is especially true for the complex roto of an object that is turning away from the screen or tracking an object that is turning.