Questionnaire download issue

We had quite a few instructors complaining about the Questionnaire download after we moved to 3.1. After extensive testing, I found that if the questionnaires start with questions which are Dropdown or Checkbox type, all of other text/essay responses will be missing from the download csv file. That's the patterns I found so far, probably there are more issues I haven't noticed yet.

The code is so difficult to debug, hopeful I can get some help here. Based on what I know, our last school year's 3.0 version seemed fine regarding the download (at least, I didn't hear any complaining).