Problem with function plot_composition()

[refinedfan]

Sometimes when I use plot_composition() function, I got the problem showing in the figure below, some of the bar is not filled to 100%. As I understand, the relative abundance should be calculated when using this function, I can not find the reason why this happens. Could you help take a look?

mycol<-paletteer_d("ggthemes::Classic_20",n=20)
p <- plot_composition(my_phylo.filt, "Domain", "d__Bacteria", "Genus", numberOfTaxa = 8, fill = "Genus")
p <- p + facet_wrap(~Group, scales = "free_x",nrow = 1)
p <- p + scale_fill_manual(values=rev(mycol))
plot(p)