Tested with version 3.7.0+180418, and geting the same behaviour, when I advance in the survey and return to the page, I verify that the rank is not saved.
Might be on purpose / a technical issue. However, I think only the developers will be able to answer this, therefore: make a bug report. You can use your forum credentials to log into the bug tracker.
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Provide your LS version and where it is installed (own server, uni/employer, SaaS hosting, etc.).
Always provide a LSS file (not LSQ or LSG).
Note: I answer at this forum in my spare time, I'm not a LimeSurvey GmbH employee.