Scorekeeper in upper left corner
That scorekeeping line in the upper left hand corner of the lessons has been changed. I find the new version more difficult to read, and keep track of my progress in the lesson. I did not see anything wrong with the old scorekeeper that required changing. The old system was very clear about each sentence, right or wrong, and the progress toward completing the lesson. Please bring back the old scorekeeper to our lessons!
This seems to be part of an A/B test that duolingo often does to see if a new feature will be useful. While these test are being conducted, a percentage of users will be chosen to be in the "test" group. They are given the new feature for (usually) a few months, and their progress and participation are compared to users who didn't get the feature. If the new feature improves progress or participation, all users will get the new feature.
So, if this feature really isn't helpful to most users, duolingo will do away with it.