Question set - multiple choice gets all the points with 1 good answer

Hello,

I've been working on a Question Set which includes 6 questions and only one of them is a multiple choice type. But the multiple choice question has been having issues whenever we test it.

For this question, there are 3 right answers except that when test it, the quiz accepts 1 answer as the ultimate right answer.

Example : 
In CasC(2).jpg, the right answers should be n°2, 3 and 7. Except that only answering n°2 gives you all the points. Which doesn't work with the other two right answers as you can see in CasC(3).jpg and CasC(4).jpg
I first thought it was a problem of pourcentage of success, but if it had been, answering any right answer on its own should give all the points. (+ I've made sure all the parameters are at a 100%.)
Moreover, when I refresh the page, the single right answer getting all the points changes. One time it was n°2, then n°7, then n°3, etc...

I have tried deleting the question and rewritting it, I've tried changing the answers, but the bug is still there. Does anybody know why this is happening and how can i fix it?

Thank you!