Quiz errors

[DDVazquez]

I'm working on Quiz slides, the only feature is when you failed a certain amount of times a question, the program send you to a previous slide and let you return to the same question you failed. the problem is when you get to the quiz results slide,the results only show "0" or "NaN" and this happens only when you were returned to any of the previous slides. this worked fine when i first created, but later in the project it just stop working and i have no idea why, I've checked everything and i cant find the problem.

any suggestion?