Hello Rebecca,
We have experienced this issue with multiple attempts when choosing the "Build on last attempt" setting is enabled. It was recommended to us by Instructure Support that we not use that setting in conjunction with allow backtracking. However, our testing seems to show that we still have an issue with only the "Build on last attempt" used w/o the allow backtracking.
Have you submitted a support ticket for your instance? It may be good for Instructure to have multiple examples.
From support:
"Thank you for your response. We are aware of the issue with the New Quizzes, and our engineering team is currently working on a resolution for it.
Currently, as a workaround, could you please disable the "Build on Last Attempt" OR "One questions at a time. Allow backtracking" in the future Quizzes?