Report Builder reports are omitting the Star rank from the Next Rank field in reports that include Next Rank as an item. However, it appears to correctly report the next rank percentage.
Based on some quick testing, it correctly shows Star in Next Rank for First Class scouts if you include at least one scout who is at or above the Star rank.
However, it appears to omit the Eagle rank for any Life scouts if there are no Eagle Scouts in the report.
Adding in one Eagle Scout gets the Next Rank field to behave as expected at all rank levels.