Looks like the error when just running facet_share is:
ggplot(df, aes(x = AgeBand, y = Population, fill = Gender)) +
geom_bar(stat = "identity") +
facet_share(~Gender, dir = "h", scales = "free", reverse_num = TRUE)
Error in unit(c(axes$y$left[[1]]$children$axis$widths[[tick_idx]], 1, :
'list' object cannot be coerced to type 'double'
In addition: Warning message:
In f(...) : NAs introduced by coercion