Why are the data missing underneath some of the must to answer columns?
There are several possibilities:
1) People may have stopped answering on that page or before -> check LASTPAGE
2) People may have completed another questionnaire -> check QUESTNNR
3) You may not have included the respective questions in your questionnaire -> check Compose Questionnaire
4) You may have renamed the variables -> check the question
5) You may have change the question time from "selection" to "multiple choice selection"
6) An error may have occured during data import -> check Collected Data -> View Data