"This month" has completely disappeared from the Leaderboard.
The new version is worse than the old one :( (27.05.2017)
Edit (01.10.2017): they finally fixed it. However it was quite irresponsible to release immature versions of the software, they should have waited with the publishing. They completely lost face by this.
UPDATE (31.05.2017): This month seems to be back, hurray! Duolingo team, please, please, please, do not do experiments on live people next time and do not release unfinished software!
Your link returns "Error 404 Sorry, the page you were looking for doesn’t exist. "
That is my fault, sorry. I should have edited this comment. Anyway, that discussion contained information on the new web page, and my (hard-worked-on) comment contained a list of changes. The discussion was deleted.
Try this discussion instead. It describes most of the changes. It has a dead link in it, but otherwise it should serve to your purpose.
I am aware that it is the new version which has caused "This month" to disappear. I am very unhappy about it and this discussion I opened was to attract the attention to the lost feature.