The similar troubles occurred in our Moodle site.
In our university, some teachers separate their questions into separate pages.
Additionally, they prohibit students from returning to previous page while taking a quiz.
Some students access to the quiz from multiple web browsers (or multiple devices, e.g. PC and smartphone) at the same time.
They use one browser to answer the quiz, and use the other browser to see previous page.
Some students using multiple web browsers faced trouble of automatically sending their answers and ending the quiz, even though they didn't click the submit button.
They were unable to answer some of the questions because the quiz ended before they have answered all the questions.
All students with this trouble are logged from multiple IP addresses during the taking of quiz.
So, I guess that using multiple devices (or multiple web browsers) would cause this trouble.
In our university, some teachers separate their questions into separate pages.
Additionally, they prohibit students from returning to previous page while taking a quiz.
Some students access to the quiz from multiple web browsers (or multiple devices, e.g. PC and smartphone) at the same time.
They use one browser to answer the quiz, and use the other browser to see previous page.
Some students using multiple web browsers faced trouble of automatically sending their answers and ending the quiz, even though they didn't click the submit button.
They were unable to answer some of the questions because the quiz ended before they have answered all the questions.
All students with this trouble are logged from multiple IP addresses during the taking of quiz.
So, I guess that using multiple devices (or multiple web browsers) would cause this trouble.