I made a quiz with matching questions in 2.9. After the quiz was closed, I noticed that one of the answers was incorrect. So I edited that quiz question and did a quiz regrade for all 200 students in the course. Expecting one a one point difference in some of the scores, I was surprised to see that almost all the students had a difference of several points from the first quiz to the revised version. I reviewed the attempts of several of the students and found out that several of their choices were now showing "deleted choices". (see attached gif)
I realize it is probably too late to get those choices back, but what did I do wrong originally? I downloaded the results from the original quiz so I have the corrects scores, but I would like to know what I did wrong in order to not make the same mistake on future quizzes.