Hi everyone. This is my first post on this forum. My issue is described in 2 screenshots below. One account is a student who completed the quiz. The other is the teacher who wants to view student's attempt. But in teacher's screenshot, there is no attempt at all. Could somebody help me with this? Thanks a ton. 
I suspect that the student has another role in the course that is allowed to preview quiz or the student role has been altered to allowed quiz previews. If a role is allowed to preview a quiz, then their attempt will not be recorded.
Thank you for your help Emma. But I have already removed student role in previewing quizzes. But the problem is still unsolved.
I did remove previewing quiz for students and it is solved. Thank you Emma :D