I found a few issues posted here on the Back navigation but i couldn't find this one (although hard to believe it hasn't been noticed already).
When i click Back to go back to edit answers on previous pages and then hit Next to get back to original page; i see the answers selected on that page were not saved.
Closed: outdated
5.4
Code - Quiz core
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It's likely this issue predates Contrib.social: some issue and comment data are missing.