A number of times now, we've had student quiz attempts with empty answers. I've managed to track it down to the fact that -- for some unknown reason -- they open up two browsers (for example one Firefox, one Chrome) and open the quiz attempt in BOTH browsers. Then they enter their answers in one of them, but when they close (almost simultaneously) the one they left blank is the one that's saved and the one that had all the answers returns the attached error message. UGH!
I don't know how or why they do this in the first place, but has anyone got any ideas on how to prevent this from happening? I tried playing with different settings, such as forcing a delay between attempts, hoping that Moodle would prevent a second opening of the quiz, but all it did in the second browser was show "in progress" and allow to "continue attempt."