Please open the original random geneator and check the counts rights of the contents.
Assume that you have 4 elements in the random generator, and 3 of them have been drawn 3 times, and one only 2 times:
3
3
2
3
The third one will be drawn unless we get another count for it. Now let's assume that your survey administration period (set in te project settings) has already startet. To avoid biassing the data collection, test runs from compose questionniare will not be counted. So, you will draw the same element each time in preview.
The same is true, if you only count in finished interviews. The third one will be drawn until one of these interviews is finished.