Spanish track recently was updated... So my nearly complete to 7th milestone tree (had just 4 circles left at 3/5) turned into a tree with 9 milestones and all progress beyond milestone 5 was wiped.

I was pretty mad! It'll take a lot of time to complete it all, it hurt my achiever feelings pretty hard. Of course, more content is more learning, but with later milestones it gets very repetitive.