FWIW I have this on Debian GNU/Linux. Normally this is plain GTK (we don't do anything about this on our end), so either there's something missing in our GTK bundle, or there's something that prevents GTK from showing those (missing font or something?).
Maybe remove/hide sections that have no emojis or add the flags.
That could be a good approach if it's a possibly expected situation indeed. However, it's again not really in our hands if it's not due to a packaging issue on our end.