I'm learning Dutch on Duolingo, and they recently updated the "Tree". Basically whenever they do that, you lose a lot of your "progress", and have to revisit (months of) previous sections that you'd already completed (because some new things are added to previous subjects). It sounds similar to what you described (very demotivating), and seems (from comments on the site) to especially affect people who are relatively newer to the site. I'm not sure yet, but I think there's a mismatch between gamification and motivation for actual learning.