Hi,
This issue is caused by empty spaces at the end of the answer input.
Please see screen-shot with annotation.
https://drive.google.com/open?id=17r5HX02QdSZgiqeug8sR6_UW9s5cmM1S
We are able to replicate this issue in the following quiz.
Blank Space in Answers
Due to the empty spaces, QSM is not picking up the user-selected answer and does not record it in the results.
Our developer will fix this issue in the next version update. Meanwhile, I suggest you to please remove empty blank space at the end of the answers.
Regards,
Kriti