Grades disappeared after individually assigning

When a quiz is individually assigned to a student, the assignment is treated as a separate instance for the selected student. As a result, grades for other students may temporarily disappear from the grade book. After the individually assigned students complete the quiz, restore all student grades in the grade book.

1. Navigate to the course
2. Click the gear icon for the quiz and select Edit. 
3. From Assign to, delete each student's name. 
4. Click Save Changes.