Move an Object problem with AR Foundation

Greetings,
I was able to generate an object on the floor using the same code as the Ar Foundation example, but I had to change it to spawn the object in the middle of the screen instead of the tactile position.
Now, if I move the object with the camera it moves jerkily, not smoothly... why is that?
Also, there is a way for resetting the tracking of the scene and start over? Thanks

EDIT: I tried the build of my project on iOs (iPad). The problem with the object moved by the camera is gone, but the tracking is very poor...