Hi @WejdanShahin
Can you clarify what you mean by a "deferred exam"?
Are the students still listed in the "Assign To" settings for the exam?
Most often, when instructors tell me that grades have disappeared, it is because they have tried to give one or mote students access to an exam/assignment at a different time, and when they did that, they removed the existing students from the "Assign To" settings, rather than creating an additional "Assign To" for the students that required different dates.
Canvas has instructions for setting up different dates for individual students at
https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-assign-an-assignment-to-an-individual-s...
