Questionnaires are submitted but not counted

Questionnaires are submitted but not counted

by Matthias Makowsky -
Number of replies: 0
I've created a questionnaire without open/close date. Users can resond only once. Answers are anonymous.

5 Users confirm and I can see it in the course statistics, they have submitted their answers.  Trying to respond a second time is refused.
But as teacher I can see only 3 reponses. Some reponses seem to be lost.
What is going wrong?

Matthias
Average of ratings: -