The returned ranking object of rankThenAggregate contains different variables holding the result of the aggregation depending on the data set.
For single-task challenges the name is rank_mean (if mean is chosen as aggregation function). For multi-task challenges the name is rank_FUN (independent from the chosen aggregation function). In aggregateThenRank the variable is named value_FUN for both single- and multi-task challenges.
The variables should be named consistently to avoid confusion.