Timeline as trigger for variable

I have a quiz in Storyline. I added 2 variables: QuestionNumber and set the value to 0 and QuestionTotal and set that to 10. (Okay, I didn't have to use a variable for QuestionTotal but I did).

The header of each question slide is Question %QuestionNumber% of %QuestionTotal% Questions. I have a trigger on each question slide to add 1 to the QuestionNumber variable when the Timeline begins. That works all as it should..... except when the learner chooses to Retry the Quiz. I have the Retry button as a trigger to change the variable QuestionNumber to 0 to reset it.

And it works, except somewhere along the way, it skips a number. It's random as to which question and to which number. It seems like somewhere there is a second timeline that starts. I do have feedback set for each question, so wondering if there's a timeline that runs on the Correct and Incorrect layers. The thing is that it will always skip a number... just one number to where I end up with Question 11 of 10 Questions. I can't find where the "second" timeline is. Any ideas?