The most common cause of this is when there's a light directly over your phone and notebook. This may cast a phone shadow on the notebook over the symbol area and cause the camera to think that a symbol has been marked. We suggest finding an environment that minimizes shadows on the page.
In addition, there may be times when the ink is not completely erased from an unselected mark. Please be sure to erase that marking completely.
For additional questions or assistance, please email us at firstname.lastname@example.org