Multiple choice survey response not answered out of 140 people- no other issues detected.

Hi,
A bit of a mystery for a multiple choice question I put out in a recent survey. It was a simple Yes/No answer. However, after checking through the data after completion of the study - I have noticed that not a single participant has answered this question.
The question was followed by a 'Why?' with an option to elaborate on their decision for Yes/No, which many people have filled in. However, it is still not clear if this was for this question or the question before.
Upon preview, you can select the answer, and according to individual responses they also viewed the answer. I find it highly unlikely that out of 140 responses no one put yes/no to this question.
Has this ever happened to anyone else before & if so did you ever figure out what the issue was?
Thanks.